I had a fair amount of fast glass with Canon but for me, one appeal of the E mount system was the ABILITY to choose smaller, but not markedly inferior lenses. Using Canon glass and the adapter will usually mean a larger, longer, heavier combination than what's available with Sony.
Lenses that I had vs lenses I now have...
EF 16-35 f/4L IS --> FE 16-35 f/4 - Sony is 100g lighter, but .4" longer, but then you add the adapter and it's significantly lighter and shorter
EF 35mm f/1.4L II --> FE 35mm f/1.4 - Sony is 130g lighter, but about .25" longer, but then you add the adapter and it, too, is significantly lighter and shorter. This is the ONLY lens switch I struggled with making. The 35L II is SO INSANELY SHARP that even a perfect copy of the Sony can't keep up. However, the Sony does render backgrounds smoother and in a more pleasant fashion. Here, I made my logical mind overrule my emotional mind and sell the Canon in favor of the lens which was native, smaller, and lighter. I still question whether I made the right decision VERY frequently. The Sony 35/1.4 is FANTASTIC, but the Canon... the sharpness... WOW!
Sigma 50mm f/1.4 Art --> FE 55mm f/1.8 - Sony is 430 grams lighter, 3/4" smaller in diameter, and over 1" shorter than the Sigma, but then you add the adapter and the difference swells even more. The difference in size and weight is ridiculous and adding the adapter makes it downright absurd. The 55mm f/1.8 is easily just as sharp as the Sigma 50mm Art (which is known for being razor sharp). Obviously the aperture difference makes this not a fair comparison, but again, one of my goals was to decrease size and weight without sacrificing image quality, even at the expense of aperture speed and this trade achieves that for me in spades!
EF 85mm f/1.2L II --> Zeiss Batis 85mm f/1.8 - Zeiss is almost 600g lighter, and nominally longer, but once again, if you add the adapter to the Canon, the lens length difference is in favor of the Zeiss and the weight difference increases substantially. This is another situation where the apertures are not the same, but I sacrificed lens speed in favor of size, length, and weight.
EF 135mm f/2L II --> Zeiss Batis 135mm f/2.8 - Zeiss is 136g lighter, and nominally longer, but just as above, if you add the adapter to the Canon lens, the picture changes dramatically. Same situation as above with regards to smaller aperture but the difference in size, length, and weight make it worthwhile.
I use my equipment quite a bit for family outings and I don't mind lens swapping. So, for trips to places like Disney, Busch Gardens, the beach, etc., I'll bring a camera and 2-3 lenses. On the very first trip we went on with my Sony gear, my wife picked up my camera bag to hang it on the stroller, like we always do, and her eyes got BIG and she turned to me and said "this is a LOT lighter". Then she inspected the bag from the outside and said "it looks smaller too" (referencing the depth of the bag - which is an across-body bag). And she's right, it's QUITE noticeable.
Again, I realize I've sacrificed some speed in terms of aperture, but I'm okay with that as I haven't sacrificed image quality (the 35mm trade off favors smoother backgrounds so I tell myself that one is worth it... lol).
Here's an image from yesterday where I was testing the ability of the A9 to track the eyeball of a running toddler using the Zeiss Batis 85mm f/1.8 at f/2. Of 7 images, the first of him standing still and the next 6 of him running, all were perfectly focused on his eye except this one (the last one) which was only off by a minuscule fraction of an inch and appears tack sharp unless you view at 100% or greater.
This is something that the 85L II could NEVER accomplish thanks to it's slower-than-everything-else-on-the-market AF speed.
Just something to think about (the size/weight/bulk thing)...