Pre skip zoro was built different.
In pre skip power levels were not defined with a structure and pre ennies lobby zoro was always one of the strongest on par with luffy and capable of defeating the main villain himself.
In post skip , zoro was sidelined and the gap between luffy/main villains and zoro increased with additional characters like law , yamato , kidd etc being comparable to him being added and taking his screen time.
Rather than having zoro and sanji "beat" BM , he had law and Kidd do that. Rather than zoro stalling Kaido , he had yamato do that.
And now loki who is one of the strongest characters to be introduced and becoming way more prominent than zoro.
I mean it took roof top for zoro to shine from the start of the post skip.