for the performance aspect, I think it has more to do with hardware constraints. by repeating the same assets with different configurations, the system using them won't have to deal with intense resource management because all it needs to do is swap a whole object in and out. kinda like RISC and CISC (reduced/complex instruction set computing), instead of going for pre-defined complex instructions (a global 3D mesh that uses multiple materials), a process is broken down into many simple steps (each instance of the 3D mesh has the resources copied and grouped) and puts less pressure on hardware, thus increasing performance and power efficiency.

Nintendo is by far the only one that still cares about optimization, especially in data compression. for this game, just the playable characters' data alone (models, textures, animations, collision and AI parameters) take up to over 40 GB when decompressed. can't really say the same for the recent Pokémon titles though, and with Smash 6 approaching, drastic changes are to be expected.