Undying was good for its time, but it's far from being the best example of a thriller/horror game. Games developed with the original Unreal Engine haven't aged well.
Or was it the best RE or SH? funny.
Every game has its flaws. The important thing is that they did it 20 years ago. I think they performed close to the best level for that period. Think of today's horror games. We still have not encountered a horror game at the level of the "undying" horror game. Today's horror games are still at the "cam scare" level. So it is extremely unfair to discuss the flaws of the game. Especially in today's conditions.
I'm a fan of the genre, so I've played most of them. Undying was good but not even close to being the best. Games like Alien Isolation, Dead Space, and Outlast are far better at the horror part.