If in PHP or JS I make a change, hit F5, and get an error, that's not any better than the IDE already showing it beforehand.

This is even worse because it can happen in prod without you ever triggering this case. For some projects, it doesn't matter because the impact of a bug is small. For most, you put a subpar, buggy experience in front of your users, waste more time looking for the cause and debugging later with upset users, and at worst cause actual damages (depending on the project anyway).