There is an argument to be made that Half-Life: Alyx runs on a "modified Quake engine". At no point was the engine completely rewritten, though it went through several major evolutions and presumably none of Carmack's original Quake code still survives... probably.

What matters is that Valve made several major overhauls over the years and is well aware of both the strengths and weaknesses of its engine and taylors its games to them. I mean, you couldn't run Elite Dangerous on Source 2, but nobody asked. Seemingly, nobody at Bethesda corporate asked if CE was capable of multiplayer (hence Fallout 76), and nobody at Bethesda corporate asked if CE was capable of half the shit that Starfield would have to provide for exploration to be compelling in the way that it is in Skyrim.

Absolutely. I stopped playing it because it just wasn't fun, 2.0 is much better. Bikes are way more usable, but I'd love to be able to hoon the cars like a GTA game.

Edit: Ok, I figured it out. You can't hammer the gas all the time. The driving works more like an actual car than a GTA game. So if you drive more like Forza, you can actually hoon the cars. Bikes are more tolerant to full throttle. Controllers having a variable input for the throttle allow you to control throttle like a gas pedal. So higher acceleration cars become drivable with less throttle and hammering gas produces a "realistic" ice rink feel, as desired. I still prefer Jackie's bike despite this understanding.