Sport is the best one. Yes I'm a heathen.
But seriously, after getting addicted to Sport mode I just can't race against the AI for an extended period of time in any racing game any more. Its just not the same and it's an area where the genre has really failed to innovate.
GT7 disappointed me because they didn't expand on Sport mode from Sport and in many ways it was a step back so it's the least played GT game for me by quite some distance. So now I exclusively play iracing and anything hosted by low fuel Motorsport (ACC and Rfactor 2).
Unless this Forza has made some big changes to the way online races are organised and wheel support then I most likely won't bother. The drivatar system is just bad.
You're one of the few people I've seen that's touched on this subject, and did so very well imo. It reflects my exact thoughts on a wider genre of games though.
Graphical and physics comparisons aside for a moment. It's an objective fact that GT Sport absolutely cleaned FM's clock when it comes to multiplayer. You don't have to look any further than Turn 10's reaction to know that they were shook, and yes... I'm aware of how cringe the word "shook" is.
Almost immediately after GT Sport came out, Turn 10 went silent for a couple of months, only to then announce that they would be taking the extra time to work on FM7, and particularly the multiplayer aspect of it. All those late game features such as track boundaries, penalties, and track marshal features were a direct result of them seeing just how lackluster their multiplayer was. Up until then, GT was basically a no show with multiplayer, so Forza always won on that front by default. That extra dev time spent on desperately trying to salvage the multiplayer on FM7 is why it's taken so long to get another proper FM. I'm sure there were some important lessons they learned from all that additional dev time that helped them with this game. (Chief among them is the overzealous banning of players for even the slightest infraction)
As to your point about it being impossible to go back though. While racing games aren't that way particularly for me, I definitely understand what you mean. Because for all the polish and storytelling that Sony's studios have perfected over the last decade. Almost all of it is entirely lost on me for that exact reason. I get the appeal of games like uncharted, tlou, god of war, etc.. but for the life of me, I simply can't spend any significant amount of time with those games anymore for the exact same reasons you brought up. Call it spoiled, narrow minded, or whatever you want. Going through the same repeated playthroughs with the AI doing the same mundane things over and over again just seems like a chore to me. It takes a singleplayer game of epic proportions the last example being Red Dead Redemption 2 to get me to play through the entire thing. Despite my repeated attempts, it seems my days with singleplayer games are largely over. Whatever that "it" factor is that makes human opponents superior to AI ones has it's hooks in me deep. My brother doesn't understand how I can play hours of a game like Hell let Loose or Call of Duty. He questions how is it that I don't tire of playing the same maps over and over, and fighting over the same checkpoints. All while playing his singleplayer games, sneaking up on the same NPC, snoozing at the same place, and hiding in the same bush.
I really wish I could get lost in all those singleplayer games and those crafted worlds the way I used to when I was younger. I'm not sure if online multiplayer has spoiled me or jaded me, but whatever it is I just can't be taken in the way I used to be.