The last 3 superbowl champions were mediocre to average during the regular season before they got hot.
This is potentially an endless, circular argument/discussion in which our position depends on where we jump into the circle.
I really don't know the answer, but your comment got me thinking.
Can a team that "got hot" and won a series of tough Playoff games, including on the Road, against very good teams in order to win the Championship still be regarded as having been "mediocre to average" during the regular season, or was it indeed a team that never really was "mediocre to average" but whose record, for whatever reason, didn't reflect its quality?
Or should we just default to Bill Parcells' famous saying that "You are what your record says you are?" If your record says that you're a 4--4 team at the midpoint of the season, then you are, at that time, a 0.500 team; no qualifiers like "mediocre" or "under-performing" are needed, it's still just "a 0.500 team." But if that team goes on to win the very last game on the last Sunday of the NFL Season, then it's record will say that it was better than all the rest, no matter what preceded it.
Since the difference between a W and an L during the regular season in the NFL can be so slim and since the rhythms of an NFL season can be so unpredictable, can we really say that a 10--6 or even a 9--7 team that goes on to win a Championship was "mediocre?" Or should we just say that it had a statistically inferior record at one point in the season in comparison to other teams that many observes considered to have been better?
I honestly don't know.
[PS: none of the above suggests that we can't pass judgment on a team as "bad" or "very good" during the season, just that it's hard to look back on the SB champion and argue that they were "mediocre."]