I'm sure a QB will come available. In the past couple years, Stafford, Wilson, and Watson switched teams. Who knows who will be available in a couple years. Maybe the Chargers and Justin Herbert can't agree on a contract and he wants out. Not saying that Herbert will want out, but we don't know who will be available.
I look at the 2018 QB class that was suppose to be so great, and of the 4 QBs taken in the top 10, only Josh Allen ended up being better than Goff. Maybe you can make the case a health Mayfield is equal to Goff. Looking at last years draft class, Davis Mills is the highest rated QB with the most TDs. Going all in on a rookie QB can be risky.