Hi and welcome to POTN,
Yeah, I wouldn't be too quick to blame the camera.
If you use the center AF point only on your camera, it's not much different from the center points on all the other cameras.
The 50/1.8 is capable of making nice images... but it's AF accuracy and consistency are notoriously "iffy". The 85/1.2 is also one of the more difficult lenses to to focus accurately. And super large aperture lens is more challenging. The 85L is slower focusing, designed that way deliberately to improve accuracy... but with super shallow depth of field of large apertures, you better nail the focus or you'll have problems.
The new T4i essenatially has the AF system of the 60D (and earlier 50D, 40D).... which is 9 points, all of them "cross type". The T3i (600D) and T2i are more like the 30D and earlier (and the 5D classic and 5D Mark II).... with 9 AF points, but only the center one the more sensitive "cross type". Using only the center point, particularly in One Shot or Live View, you will see very little difference. If you manually select some of the outer points on your camera (or 30D, 5DII and earlier in these lines) you will see slower performance, a bit more hunting in lower light.
But, even those simpler AF points are usable and can be accurate. For best accuracry, don't use AI Servo (for moving subjects) or AI Focus (not really a focus mode at all). Use One Shot... Or even better yet, use Live View... though it's slower.
So it can be down to technique... But lenses are also important, a big part of the focusing accuracy and speed equation. I also think upgrading from the 50/1.8 to 50/1.4, Canon or Sigma (though the latter might need calibration). USM lenses (or equivalent HSM in Sigma and USD in Tamron) are what you should be looking for. In general, those are faster and more accurate focusing. There are some exceptions... such as the big aperture lenses, which are USM but tuned to focus more slowly for better accuracy.
Bokeh or background blur is a factor of several things... not just the size of the aperture. One is the design of the aperture... lenses with more blades and sometimes specially curved blades give a more perfectly round opening and can make for nicer bokeh. (The 50/1.8 has five blades... the Canon 50/1.4 has eight and the Sigma 50/1.4 has nine. This makes for nicer bokeh.) Focal length and the distances you work from are another big, big factor... both the distance from you to the subject and the distance from the subject to the background, determine how strongly the background is blurred.
Full frame cameras, such as 5D Mark II, don't actually change depth of field... but it feels like they do. Using the same focal length, you work in closer to your subject to get the same framing, so will find that depth of field seems shallower. Also, full frame cameras give smoother transitions and gradations, which can be a factor with "good bokeh".
If you don't already know it, look into "hyperfocal distance" and "hyperfocal focusing distances", get and study depth of field charts and how DOF works. You need to learn this, if you intend to work with big aperture lenses near wide open.
Really critical focus with AF lenses might also call for a camera with focus Micro Adjust feature. Your camera doesn't have that. None of the Rebel/xxxD series have that feature, where you can fine tune the focus accuracy of up to 20 lenses on your particular camera. 50D has this feature, 5D Mark II and Mark III do, 7D does.... so do all the recent 1 Series cameras. But, you also can have camera repair service and adjust any camera and lens to perform to their best. Incidentally, Micro Adjusting lenses is one of the places where we learned about the AF problems with the 50/1.8 lens... It's nearly impossible to calibrate that particular lens with much accuracy. It's just too inconsistent.
Also be sure to remove any and all filters from your lens, for focus testing. Filters can soften an image overall... or even cause focus errors. Using a matched lens hood might help, too, by keeping obllique light off the lens (certainly can't hurt).
Don't mistake lens softness for focus issues. For example, both the Canon 50/1.8 and 50/1.4 are not at their sharpest wide open. When I want as sharp as possible, I stop down my 50/1.4 to f2.2 or smaller. Larger apertures are usable, IMO with my copy of this lens, just not quite as sharp. Most lenses benefit from stopping down a little.
Use a tripod. It's a more thoughtful way of shooting anyway.
At some slower shutter speeds, you will need to use mirror lockup, too... or risk camera shake blur.
Post production comes into it, too. All images need some sharpening in post... usually the final step once other editing is complete, and tailored to whatever size/output is intended for the image.
And, there's no avoiding it... some post is needed with most images, regardless of camera or focusing accuracy. I often do selective sharpening and/or even add some blur to parts of an image, when it's necessary. This allows me to use sharper apertures and/or shoot moving subjects with a little more depth of field to forgive slight mis-focus with AI Servo and fast moving subjects. There are limitations to what optics can do.... That's were some additional post production can help.
Also, you need to have reasonable expectations. If you are looking at 18MP images at 100% or larger on your computer monitor, that's sort of like making a five foot wide print with the image and viewing it from 18 inches. If you walk up to within a few inches of one of the old masters paintings in the Louvre in Paris, all you will see are bruch strokes. Now, I shoot mostly sports/action. I use the center AF point much of the time, along with AI Servo and mostly fast focusing USM lenses and Back Button Focusing (with AF lenses, a common sports photographer trick). This allows me to get acceptible focus in 95% or better of my shots. I have to work at it and do better when I'm in practice and shooting more familiar subjects, but I'm in control and it's down to me to do my job getting things in focus.
In the end, I don't think your solution is a different camera. More likely it's lenses and techniques... learning to get what you want out of the camera you've got... and fitting it with some better (for your purposes) lenses. Using manual focus lenses on modern AF cameras is tricky... the cameras just aren't very "manual focus friendly"... they don't have many of the features to help you focus, that vintage cameras had built right in. There are special focus screens available for most cameras, including yours
. That might help, but needs to be installed and can have some effects on other camera functions (in most cases, spot metering is no longer usable). Adapting vintage lenses, it can help to have the "chipped" adapters, too, that will allow Focus Confirmation on your camera to work... They cost a little more but really can help with focus accuracy. I'd be a little concerned about the quality of lens adapters, too... They are often made cheaply and there might be some variations. They have to be a very precise thickness, to properly adapt a lens for accurate focus. Some of the other camera models have bigger, brighter viewfinders, too, that can help.... and have more easily interchangeable focus screens that are cheaper (such as the high precision Canon "S" stype).
Another thing that might help is an Angle Finder... this has a built in magnifier to allow closer inspection of focus accuracy right through the viewfinder. But, Live View with your camera's LCD screen or the add-on monitor you have does much the same thing. An angle finder is all about focus precision... but is most often used on a tripod during fairly deliberate shooting. Besides the Canon model shown at the link, there are various 3rd party that are good, but less expensive.
Finally, I gotta say... I've been shooting for 30+ years and today's AF systems... even the simpler ones such as in some of the Rebels, my old 10D, 5D series prior to the Mark III.... are better, faster, more accurate than I ever was using manual focus lenses on my old cameras. Good AF lenses (again, look for USM in particular... or the 3rd party equivalents) on your camera would likely nail focus a lot more often and far faster than I ever could even with the best vintage lenses and cameras. In particular, for portraiture I'd suggest looking at the 50/1.4s, 85/1.8 or 85/1.4, 100/2, 135/2 (if you have a lot of working space) and possibly the Tamron 60/2 (though it's a macro lens, and not USD, so will be slower focusing).
Portraiture is one of the specialties of photography that simply doesn't call for fast and fancy AF... So, I'd suggest keep using your camera and work on other factors instead.
