Kart... an interesting perspective on GTS vs. PC2. But have you considered that, as a fan of GT going back several games, you are perhaps being a bit over-indulgent, like you would with an old friend?
I agree with several things you have said, but I find it hard to come to grips with GTS's low speed grip/tire model. On the edge, yes, it can be consistent, but I have a big problem with low speed grip (launching is ridiculous, and that is indicative of what is going on at very low speeds when taking tight hairpins, or recovering from spins etc.).
And yes, I find GTS's sounds much improved in some cases, and PC2's has some underwhelming cars, but taken as a whole, I still really can't get over the vacuum cleaner analogy. There are some cars in PC2 that are deafeningly visceral, something hard to find in anything in GTS.
But what is more puzzling is the complete lack of any decent track limits/pit penalties, returning of position after belting someone out the way, and the basic complete lack of any semblance to real racing in GTS. Is turning on the PS4 and booting up GTS more a way of getting away from those things for you, or does it not bother you that GTS seems to provide cars and tracks (and damn few of the latter!) but seems to basically not care about the rules of the sport?
Collision physics in GTS seems designed to not cause much disturbance to either car, but the slightest touch in PC2 tends to have pretty close to real world consequences. Are you happier with GTS simply because it is an escape from real racing, whereas most of us interested in the sport are more looking for a game that gets us closest to something we DON'T get to do in real life?!
I agree visually, GTS's real tracks are gorgeous, but again, does static time of day and no weather, no track rubbering in and the rest of it make it worth while? Watching the dry line come in as the sun goes down after a shower is, IMHO, well worth a bit of graphic compromise!
I am afraid, as a long time GT fan, that GTS is likely my last. PC2 may well have issues, but for those of us that are looking for something that acknowledges the sport, not just provides a sandbox for gamers with cars and tracks but little else, once you play PC2 it is hard to go back to GT. Practice, qualy, weather, race rules, detailed tuning, real life tire selection, AI that challenges you, all the things we wished GTS was going to bring to the franchise and never showed up, it has finally become too much.
I'm looking forward to the new 'ultimate' AC release. Perhaps time to give that handling model a try.