Then place the restrictions on the events, have a classic cars race that restricts tyre choice to period correct tyres only. Don't restrict the cars themselves.
So you want to restrict choice even further so that you can't race what you want anymore. Part of the charm of Gran Turismo has been that you can take what car you want, tune it how you want, and race it how you want. All the game needs is a decent enough rule set in place for the events that will restrict the themed events correctly.
Correction, you don't want to waste your time. I like having the choice, and if I or anyone else wants to put racing slicks on thier Dodge Charger Daytona, why not? If the game already has period correct tyres for it and forces those in the Muscle Car competition, whatever that may be called (assuming there is one) then there's no problem with having that choice surely?
How would a better tyre model solve the problem if what you really want is to restrict choice and to not be "wasting your time" choosing tyres over all of the few moments that takes.
I don't want to sound argumentative, but I really don't get your logic here. The worst part of Forza Motorpsort 7 was that they put too many class restrictions on the cars, when you bought your Hot Hatch or whatever other type of car, you could only enter it into races specifc to that class.
It destroyed the feeling of ownership and that car being unique to you, your creation, that previous games and Gran Turismo games have had in the past. If they had created a well balanced variety of events with a good set of restrictions they could have still had those class specific races but they could have provided so much more freedom in the career mode too. It was a bad game design choice.
Instead of restricting options further, I think they should blow them wide open, we won't get changes to the degree I would want, but I'd like far more choice in tuning. And if a group of players decide that in-game resto-mods are their thing, then so be it. There's nothing wrong with kitting out a classic car with modern suspension, brakes, racing slicks etc. and racing it against modern cars, in the right events. What you are suggesting makes such possibilities impossible and there's very little logic to it.