Because when someone says it shouldn't be a class feature says it should be a magic item a fighter hasWhy do you want the OP's question to involve magic items? Why can't it be about class abilities?
But no one is saying a mundane warrior and mundane thief should be able to defeat the monsters of the MM without magic items.How? Because no one is saying they're required to have magic weapons. If other people in the group have magic weapons, of course the fighter should have them as well.
Everyone says that the magic items aren't required but then creates a world with a magic items that could required.
