> I don't think twitter is crappy because of cache misses, I think it's crappy because they don't have a solid understanding of what their code is doing.

It's my hunch that you have little idea of what the code-bases for twitter are like, nor what factors are at play that affect usability issues.

> If you build your game on an entity-component system, you can't "just refractor" that to make it contiguous.

Moving to object pooling of components is very do-able. There might be some extra work, like extracting a generic matrix hierarchy and physics primitives out, but you'd only do such a thing if you found that d-cache misses on v-table lookups, or if i-cache misses due to update code churning were of real concern... and these could realistically be mitigated with homogenised object pools for the particular use case... though usually yes.

Edit: I'd expect anyone on an engine team, or technical programmers at a game dev shop, or maybe even someone working on a browser renderer to have such knowledge from day 0, rather than the average FAANG employee.