You ok there?
Despite everything you said there’s plenty of high performing UE4/5 games already out there.
If you don’t have the skills and knowledge to make your projects performant might I suggest you lower your expectations of what you should be making on your own?
At least in the AAA space we have in-house render programmers and engineers helping us solve all these problems as they come up and we often have to make custom tech here and there, but still the engine handles 90%+ of all our needs, which beats making our own engine any day.
Epic is very concerned with performance and user experience, but a lot of UE5 shiny new toys are actually EXPERIMENTAL still. You might wanna look into what that means.
At UE Fest 2024 some Epic devs I talk to mentioned they are actually looking into making a new Tree Asset Type that would handle all the common pitfalls of Nanite Foliage and foliage movement that seems really promising. They understand foliage currently is a big unknown for many studios.
But people; you’re more than welcome to not jump to the new experimental features right away and continue working with the old proven methods. Foliage with LODs and Impostors at the end still work!