For me - it doesn't matter what tier you put him in.
It doesn't matter what you think his ceiling is.
It doesn't matter how you A/B compare him to other guys making top QB money.

Is he the best chance you have right now for getting your team back in the playoffs?

Is there a can't miss candidate in the upcoming draft that you are certain will be better?

Is there a pending FA looming that you're willing to overpay who will be better?

NO?

Pay him - and don't worry about what he's shown or what he deserves. The market dictates that QBs who don't suck get paid very handsomely. And he fits the bill.

---