I have also been looking into the 28-300 Canon. I have a Tamron version, and I am not happy with it. It is very much out of focus at the 300 end, and partially out of focus on the 28 end. Didn't notice it until I pixel peeped. That'll teach me.
But there are some excellent people on this group who have the Canon 28-300, and I have asked one of them to post a test pic at 100% crop, and it was in sharp focus. The Tamron is good (if you get a good one) as it is a lot lighter than the Canon, but it seems very hard to get one that focuses well. A search of the net will confirm that. I was tempted to go to a brick and mortar store and test out their stock of Tamrons until I got a working one, but since I have seen the 100% crop on the Canon, I am saving up my funds to get the Canon.
I have had several lenses, and, like you, don't want to keep changing lenses, and missing an photo because having the wrong lens on the camera. My only difference is that I am on a full frame camera (5D3), but you would need to think about the 28-300 on a crop is more like 39-450, so it definitely isn't wide angle at that point.
I do have a 16-35mm L, 24-105mm L, 70-200mm F2.8 IS II, 100mm L Macro, 50mm F1.4, and that Tamron. I recently sold most of my non-L lenses as I didn't use them any more. I have considered selling the 70-200 to help finance the 28-300, but just can't bring myself to get rid of the 70-200, as it is a fantastic lens. I have thought about carrying the 16-35, and 70-200 as the main kit, but of course that misses the 35-70 range. Even if I got the 28-300, I'd still need the 16-35 for really wide angle.
So, I too am in a dilemma, not the same, but a variant on it. X-Tan on another thread here has been really good, and he has posted tons of excellent photos that he has taken with the Canon 28-300. There are a couple of good posters on that tread. You should take a look. The link is: https://photography-on-the.net …showthread.php?p=16047692
Good luck on your quest.