I keep reading the argument that if you hold a substantial amount of Bitcoin or if you invest big quantities monthly, you won't care about fees.

But what about all the people that are starting or will start out investing into Bitcoin? High transactions fees will push them away from investing or DCA.
And i haven't raised the argument of Bitcoin as a currency. I know it's meant to be moved slow and as a store of value, not daily transactions. But even then, if you intend to buy Bitcoin every month, costly fees are painful.