I wouldn't call the P-47 "underestimated". They are very capable, and I'm usually flying a D-11 if I'm in one. Trust me, NOONE outside of a "Two-weeker" will see a D-11 and think "this one's gonna be easy". I ain't buying that, usually if one is seen, the FIRST thing that should pop into your mind, "this person more than likely KNOWS what their doing."
If I'm in a Spit1 or Hurry1, I find more "cockiness on the cons part". These two are WITHOUT QUESTION the most underestimated planes in the bunch. People do stupid things matched up against a Mk.1, as "they won't catch me", "those 8 - .303's won't do much damage, etc."
Then again, with all of the bravado it's tough to tell. I recall getting into a 1 vs 1 with a "certain" D25 and it ran from me to a buddy, only to turn around in the 2 on 1. I guess it comes down to the individual's flying style more than anything.