Over the years many people built clones of things like Twitter, Dropbox, uuhh. Loads of things really. The core of Twitter is trivial, it's basically like my first PHP tools creating shoutboxes for websites.

Then the next challenge is scaling it to the world - and Twitter themselves struggled with that, the first years were full of fail whales, or stories of servers churning for ages whenever Justin Bieber made a tweet because (for some reason) they updated everyone's feeds even if they weren't actually online / looking at them.

But solving that also wasn't what made Twitter or Facebook popular, and no LLM will ever solve that because none of the successful software projects were successful because of code, code volume, development speed, number of people involved, or anything like that.

(That said I am convinced you can do the same amount of coding with less people at good enough quality, and said quality will improve over time as we've seen in the past ~2 years. The providers just need to add the software quality guardrails that we as software engineers learned over the years, and I'm sure there's dozens of companies working on just that)