Combat-wise, no one's more well-rounded than Zoro after Luffy.
I'm not sure you understand what this is means.
Well rounded means a wide range of capabilities.
1. Can X fight a brute force battle and a tactical battle?
2. Can X battle in the air and/or underwater?
3. Does X have both blunt and cutting attacks?
4. Can X use physical type and also elemental type moves?
5. Can X fight well both unarmed and using weapon?
Etc
Zoro always brute force things, but he can also fights tactically (vs Pica & King). On the other hand Usopp mostly go tactical. This criteria alone made Zoro "more well rounded" than Usopp.
But he definitely isn't more well-rounded than Franky who have both physical & elemental attacks, fights well unarmed & armed, can do both blunt & cutting, for example.