Occam's Razor just means the simplest option is usually the better option; The usually matters. I'm not sure what you mean by the entropy sentence. The difference in 128 vs 256 bits of entropy only applies when you think someone might bruteforce their way to getting your private key.

No it isn't, what happens when you have a brain injury that makes you forget your mnemonic phrase? What happens when your forget it as you age since as you age your memory gets worse.