I don't think the QB you take has to be better than Goff, rather just as good as Goff. You certainly hope they are better though if you are taking one. My reasoning though for being as good as Goff is the benefit of the rookie contract that comes with a Young/Stroud/whoever. If you can move on from Goff in a year and have 2-4 seasons of a QB on a rookie contract, playing at least as good as Goff is now, I think there is some merit to that. Let's say you drafted CJ Stroud and in 2 years time he proves to be as good as Goff or only slightly better, but you get Goff's $31 million cap hit off the books, minus the $5 million in dead cap if he's cut or traded, I think there is benefit to being able to have that money available to you for 2-3 seasons and load up the roster during the off-season. The rookie contract is the game changer we never were able to have under the Matt Stafford tenure.
All this said, if someone like Will Anderson or Jalen Carter was a game changing, all pro player on defense, I wouldn't pass up on one of them just to have the benefit of a rookie contract. I'd probably take one of them. Though the argument could be made that you can get the best of both worlds by trying to find a Chandler Jones or Khalil Mack type of player to trade for while drafting your QB, thus giving you both a game changing defensive player and the benefit of a QB on a rookie contract.