For all those naruto watchers, fans, you all are aware of Might guy.
For all those who don't, Might guy was like top commander level, but once he unlock his all gates, he was able to equally fight and even overpowered the then strongest in the verse in expense of being a handicap forever.
Do you guys think Jinbo will unlock all his karate man gate n fight Imu?
First you must constitute "what" a Might Guy is, his character concept, and equalize it to One Piece.
Otherwise the classification will be too broad & not specific, we can name anyone.
1. He is a martial artist with mostly no weapon.
2. He has limited Chakra/not talented in other usage of Chakra/can't access all Chakra.
In OP equivalent, not CoC users.
3. He has no bloodline power.
In OP equivalent, not Devil Fruit users.
4. He has no tailed beasts.
In OP equivalent, not Zoan users (that has will on their own).
5. His power starts from mediocrity.
In OP equivalent, not characters whose childhood is already super (e.g can destroy/lift huge boulder).