Except you don't look for your 1B to be "league average". Their primary job is offense. You look for "league average" hitters at non-offensive positions. Your 1B is there to create runs.
Of 1B's last year with 400 or more PAs, his 97 RC+ ranked 29th of 36 hitters. Factor in his below average 1B defense, he drops to 31st best at 1B. I mean I guess you can say they picked better than 2nd round pick Gavin Sheets, who is dead last, right?