I do have a lot to say on this topic and I'll try to make it as constructive as possible.
It does feel like ever since the launch of GT Sport, there has been an identity crisis at the very heart of GT that stems from the divide between the single-player content, which mostly uses road cars and allows you to tune each of them to your liking, and Sport Mode, which focuses almost exclusively on grouped cars with BoP and a fixed setup. This has also caused a rift in the game's fanbase, which has divided itself into several camps that each stick to their part of the game and never venture out of it.
None of this is helped by the fact that the game seemingly doesn't want you to actually have fun with the hundreds of cars it advises you to collect. Sure you can race them against slow-as-molasses default AI or overly aggressive Sophy if they even have suitable events for said cars (and a good handful don't), or you can pray that a PP-limited open lobby is up so you can try and build it to compete... and get blitzed by a random engine-swapped car that's 200 PP lower than it should be.
It just doesn't make sense to me, almost every update adds a handful of road cars that would be absolutely brilliant to race, and sometimes they even get cool-as-hell customisation options that reflect real-world racing variants, and then they never see any use in Sport Mode, because apparently it's much more important to cycle Gr.3 and Gr.4 twelve weeks in a row, and so nobody learns anything and nobody reaches out of their comfort zone!
Those two weeks with the AE86 and 22B tuning dailies were some of the best weeks in this game's life, you had people learning all sorts of tuning techniques and the leaderboard times constantly updating throughout the week as they put their theories to practice, and the best part is that they even convinced some people who previously didn't understand tuning about its merits! I just struggle to comprehend why PD would see that, decide it's not worth continuing, and go back to the same repetitive formula they've milked dry for the last 9 years...
To build on
@Nebuc72's point above, I definitely think a quick match-type mode (like we had in GT6!) would do wonders for the replayability and variety of GT7, because despite this game having almost 600 cars now, it really doesn't feel like it most of the time. Another thing we desperately need in order to bring back that GT feeling (and you knew this was coming) is the re-introduction of
Shuffle racing to open lobbies. Think about how many cars you've never driven in a GT game. Now think about how many you could've fallen in love with, had you gotten the chance to drive them in a semi-competitive race. Shuffles are the key to everything.