I can agree that most engines suffer from certain malfunctions, but obviously Gamebryo/Creation is one of the worst engines today. FO4 is broken real bad, game has no optimization for what visuals it presents. Putting Skyrim SE on x64 rails only (maybe) reduced crashes, but visually it basically the same as it was, how can it be step anywhere at all? I don't see any progression here, and my only guess is that Beth doesn't wanna change engine, because it's too expensive and crew will have to learn working with new software, and even if it's much better, it will stall most of their projects. They rather release games on old broken re-branded engine, and let customers deal with issues, as they always have.
For reference GTA V engines are almost perfect, game only suffers from insignificant memleak issue, and it only occurs during multiple data reloading, though it's not the only good open-world engine out there. As for the "living" TES/FO worlds, can't say it's very lively to me at least, same ol' routines happening over and over again, plus coding can be done much more resource efficiently than the way it's done.
Constantly having lots of gamebreaking issues across 6! different games released by Beth on it doesn't really play in "bad coders" argument, by that time, they should have learned to solve at least half the issues, but every time things get even worse, what's to blame here if not the engine? It is obviously technically disabled soft.