Oda wants to portray Zoro on similiar level as Luffy, Kidd and Law despite not being a pirate captain
This should also transfer to Zoro's opponents (mainly, Mihawk)
Mihawk will be on par with Admirals and Yonko's
Because Zoro is versing Hawkeye
That way, even though Zoro did not the same opponent as the captain trio (admirals), he will fight someone on the same level (Mihawk) after beating Samurai Ghandhi (as heat up, and, to snatch the Shodai Kitetsu)