React brings some complexity but at the benefit of better state management and DX. If you have ever worked on large projects where each button has a click handler to do 20 different things, you will find that it's easy to miss some edge cases and have state drift.
Postgres has a worse implementation of MVCC. It results in more bloat being produced, and slightly slower updates in a highly concurrent environment. Most businesses don't operate at the scale where this matters. But on the flip side, the tooling and developer experience is much better.
Other fads have the disadvantage of being easily identifiable and avoidable. But AI chips away at what it means to be human. Now imagine if every comment in this thread is not a real person, but made by a LLM. Get any Truman show vibes?
Complexity doesn't necessarily slow down feature development. In my experience it reduces the project longevity. At some point it will be too big and complex to rewrite all the while more glaring problems emerge and cannot be dealt with.