As a moderate but nowhere near complete SMT veteran, I will say this:
Devil Survivor-level of being able to choose what to inherit is too damn convenient and broken. Non-deterministic inheritance system isn't perfect, but the idea of the knowledge and application of mechanics and theory tilting the odds in your favour is something I find to be far more rewarding than what Devil Survivor did. And it's also magnitudes better than the deterministic system used in SMT2.
Removing game over-on-main character defeat is not easy to do without killing the Megaten feel. When your main character is roughly equal to other party members in mechanics, like Serph is to rest of the DDS cast, Maya and the P2:EP cast, or El to the other 2 humans in Last Bible, you can get away with not having game over on protagonist defeat. But for a P3/P4 style protagonist (special snowflake being able to change personae) or a Nocturne (the only human in the party), or Strange Journey (only human in the party), or Raidou (see preceding two), I find it to be a critical aspect of the atmosphere and SMT's general standard of being tougher than a pushover.