As of now there are people who think zoro is weak because he has not had any extreme fights. They need to see it to believe it. That is their own way of interpreting one piece. Before the timeskip the only person we saw train was zoro, and yet all the other characters got stronger.

Its likely that even tho luffy is the only one who got development, the others got the same development as before the timeskip. So when the characters you think are weak defeat opponents that they shouldnt otherwise... if that makes you dissapointed then its on you.

Zoro can fight whoever, and grow stronger during the fight same as luffy. Never do i see zoro, being a coward in a battle. If zoro fought the characters luffy fought then, zoro would develop as much as luffy.

The issue is people truly believe that the rate of development for zoro sanji is completly different. But in reality Its because of the situations they are put in.

If nami or usopp got to train with rayleigh imagine the type of characters they would be now.

If zoro fights king and defeats him, its likely that people will believe king to be weaker than katakuri, just because it falls in line with how they interpret one piece.