Candescence
Member
There is only one hard story content in the game and no amount of 5* will save you from the hell that is Camelot. You need an all-rounded Servant pool of varying types to beat that content.
You can solo Tristan with fucking Asterios, and make NP-spammer Mordred (and I mean fire her NP every fucking turn) unable to do shit with a team built around being able to spam Asterios' NP, and he's a one-star Berserker. That's pretty much proof that stars don't mean shit if you've got properly-prepared Servants and the right team composition to deal with a problem.