Sorry that you think I'm being rude (which I am), I just can't stand it when people give off something they think they "know" as fact just because they read some vague technical stuff somewhere.
The fact is that engines have been gutted and revamped, adapted, rewritten, etc since the dawn of time. And neither you nor me know shit about these things. Maybe they make a completely new engine as you say, maybe they just put in new stuff, maybe they adapt it god knows how. So unless you are, idk, Durante on his alt acc or someone from Naughty Dog, there is absolutely no reason to believe anything you say.