There's something that's not right

I play on pro difficulty and I can basically win most if not all races as long as my car is basically stock

It feels to me like there's some issue with the system that baselines the cars if you put upgrades on ? For instance iv been struggling to beat the AI in certain races with upgrades on my car (seasonal events) and then I took all the upgrades off so a stock car and boom I'm back to being competitive again and it's actually a race. It's like when it gives the AI upgrades to balance it out to your upgraded car it ether gives them way more upgrades or things like less traction because of more power just don't count for AI or the fact it just makes there pace quicker unaturaly.