Tebow was 8-5 with a big playoff win in 2011 on a team that started 1-4, and with insincere support from management. He is above average.
That doesn’t make him above average, that makes him on an OK team. Trent Dilfer is generally considered to be the worst QB to ever win a Super Bowl. He went 11-1 on a team that was 5-3 without him and nobody thinks he’s above average. And his career completion percentage is 55.5. If 55.5% isn’t above average 47.9% is DEFINITELY not above average.