You seem to be describing some technical issues[?] though I rarely see them. I think as someone involved in tech I'm often amazed at the incredible feat of engineering sites like FB represent, metrics like 4,000 photos a second uploaded, millions and millions of posts an hour, etc.
In terms of UI, it has mostly just become a bit of a cluttered mess due to all the different revenue mechanisms: ads, promoted posts, inline product placement, etc., but there's only so many design models for something like FB. I'd contend that Amazon has it share of UI/UX issues, trying to present so many products, services, dealing with 3rd party stores, upsells, cross sells, some customer support service buried several clicks away.
Both have their share of cruft, and excessive content bombardment.