I was using Mayfields season as a recent, generalized example as someone who came in on a 1 year "prove it" deal, and earned his spot. Not as an exact baseline for where Darnold's stats need to be.
But, as long as we're taking a tangent. There is no way that Baker is "definitely not a top 10 QB." Last year was his first year with a new team/playbook/receiver corps and he still ended up as one of the Top 10 QBs in both yards and TDs. He had a better regular season record and went further in the playoffs than HoF GOAT Tom Brady took the same team just 1 year prior.
He's still outside of my personal Top 10 until he can show that it wasn't a 1 year fluke. But, you have to at least acknowledge that it's close, and if he shows repeated success, he's probably there.