I always do. The fallout community, like so many fandoms for vintage games, is wrong on most details even if they are right to love those games
Fixt is actually not a purist mod (not even the “purist” version). It added a lot of new or altered content that still needed to be edited out of ports that used fixt as a base (fallout et tu among them), along with an avalanche of new bugs (which you have already experienced)
The fallout 2 engine is also not a completely different engine. It is a direct continuation of fo1’s engine and any game mechanical changes can be reverted. Fallout et tu is akin to the mod that ported Baldur’s gate 1 to bg 2’s version of the infinity engine (baldurs gate tutu if I recall correctly, its no longer necessary thanks to the enhanced edition releases). Sure, you can use it to mix content from the two games together but the real benefit is a codebase that has been maintained over the years