I think Forza auto-engages KERS all track long without limit, that's why there's so much torque. It's probably not even really "engaged", it's just a different torque curve for the engine that looks like a normal one mirrored horizontally (like an exponential function turned 180°). The Porsche 918 Spyder's looks like that in FH2.
DRS maybe is handled automatically at certain speeds like the active aero rear wings on supercars. Hmmm... but then you'd have almost no downforce on super high speed long corners... not sure how that works.
Anyway without any KERS or DRS our times couldn't be that good.
There's no KERS in the E23, it's a forced induction electric hybrid, if you're not McLaren this year, you can have electric power for the entire lap. I think in Forza you just get full power all of the time, whereas perhaps only Mercedes could run full revs and electric for any length of the time.
Regarding your other post about spinning out at 160mph in a corner if you turn to much, I agree. I think there's something wrong with the physics of some cars, particularly the E23. The back will come out at speeds when downforce should be keeping you on the road when you haven't increased throttle.
Have you tried the Peugeot 908? I could not drive it at all, I'd try to turn a corner an it would just spin. This is when I decided the E23 wasn't that bad.
The problem is basically what Alan from Team VVV says in this video
https://www.youtube.com/watch?v=EiNM-1r47mA
PCars has more grip, but Forza loses grip in odd ways. There's a Risi Ferrari F333 SP, I can push that in FM6 same as the 787B, they just grip. It's why I think sometimes the physics are odd.