I try to explain a suggestion at the end, but if you want to know background you can read the first part. I provide reasons shortly before the conclusion based on the recent 2 pages of discussion.
Start ..
Well I would say its ok he races street cars and non street cars. One of the things I do and I do not want to get into the business of saying "Oh and I RATE IT! NUMBER ONE! Thats right I rate my experience of doing x, y z, number 1..."
We must not fall into the trap of that - its that I do something at all that you must note. And so it is with this.
So I say, no pretext, one of the things I do in this game is I select random cars (but not track usually that would be silly) from the menu in content manager, and I use that car. No ifs, no buts. I use it. Like, 7 times out of 10 lol. If that is a road car then that is what I am doing. If I truly somehow do not like that car I delete it. Most of my fave cars are Kunos cars and I do not like to add many mods. (2 vrc bently and 1999 kart series car, then rss mods, and then 1 sean clarke updated mod to 1.7/2.0 I never found any of his any good tbh but this one drives like the one in ACC mostly, so AC can indeed be that good; Kunos cars I think are under-rated tbh, and I trimmed my list of Porsches no offence since it actually allows me to drive the Kuno's cars I like most MORE lol... I like rsr 2017 race car and deleted any other rsr mod even the Ben-o-bro mod which is not a modern car; but I also use the Kunos Porsche street cars of that era and its all nice, as Porsche has that progression of era's in the game - thats not to be sniffed at in my book; so this is what I mean, so I am looking for 'peak experiences' and I also like fluffing with mods, but long term I try to keep the experience high thus I delete the chaff or non updated/suitable cars, i.e Kunos Lotus' cars, only kept 4 of them they didn't ever seem finished but the ones that were oh my, its good; this is no disrespect) So that is indeed an example of a road car right there too with the Lotus cars, some I deleted yes, but the few I kept have a place and damn its good.
You can indeed have high quality street cars in this game and I like racing them, too. I select a track and if the car even remotely seems like it will go round it correctly then I use it. This is down to probably 2 things. You can drive cars and race-cars and that I do not mind challenging myself. I have also at times deleted road cars I know I will never use.... an example is a hypercar I simply could never set up correctly for a lot of tracks maybe it was never updated but I deleted it. I liked the look of the car and everything, good brand, but because it served no 'game purpose' I deleted it.
conclusion ...
1 Maybe then the advice is to expand the list if that is possible, because I think having road cars and making use of them, from more brands, even, is a solid idea or underpinning of what they can do, so I think its good to do it and tie a system or progression to it; not sure if that unlocks like in GT (lol I do not rate those games I did play first one a lot though back in the day); but will admit that it being tied to upgrades was a really sweet thing that at least does not limit racing itself.
2 Despite that aspect of yes or no with progression/system, I think having road cars with race cars is a good thing. So both. All forms of progression have been done i.e lousy road car, semi decent road car x 5, good road car, race car progression unlock. I do not think it needs to be like that, I think mostly they should focus on a career/race system that goes up in tiers. The best aspect of AC1 is the tier race systems you can make. This is what they could do.
3 -- You do not need to segregate road/race cars I think, but you could separate and define them more I suppose in their respective areas beyond the 'freeform style of the game/menu's area... For this example I point to something like NBA2k2022 where you have the menu's and one is every team v every team, another is online another is guide a club, etc, so it has everything but some modes make it limited.
3a this would then mean that the OP, could avoid the cars he wants to avoid or modes, but he is never fully locked out of them. The worst thing about games these days is having a store front on the main menu - I think its despicable, so if he wants to spend his time in career or just in freestyle so be it, I am not sure what plans AC2 has for its front end, but I think road cars should exist in there with street cars. In some ways there may be modes where they blend beyond just racing. Sometimes I wonder if an online mode could have a free-roam map, then you flash headlights at each other or something. Just spitballing.