I think Cyberpunk has a good basis but as you say, it's heavy weight; they did increase or tweak crowd density in an update I think, but also it's a PC game so it can be modded and improved as hardware gets better. The challenge - and you already see it on lower crowd density numbers - is getting enough unique and different characters. Cyberpunk seems to have a number (dozens?) of NPC characters making up the crowds, but it gets repetitive and you frequently see identical ones.

Procedurally generated characters would already improve that, and some games do have it but they tend to pick from a fixed set of animation and behaviour stereotypes still. More of those stereotypes make it better (think GTA), but it's still fixed.

I don't think going all in on procedural generation or even AI would fix it though; especially AI has a tendency to go for a mean / average character quickly. And in video games, you still want predictability.

That said, maybe a different visual style (lower fidelity or 2d) would work.