The bruises are the same they both had before the fight started, though, and I don't remember other cases of Zoro going all out and sheathing swords unless it's for one specific move, after which he unsheathes them again.
So while the huffing and dialogue, as well as the sweating, suggest the fight has been more than casual, there is evidence of them, particularly Zoro, not going all out. Zoro not having an easy time and Zoro still not going all out are not mutually exclusive.
And I don't mean it as "Zoro is much stronger because he's holding back", but as "Why the hell is he, Oda?". As a reader, I do want to know.