First it’s important to highlight the different types of speed:
Movement speed~agility, and mobility
None of these are significant in Zoro’s fighting style, but it’s fine as he utilizes 3 weapons for a more stationary defense
I’d argue that his mobility is in line with Oda’s remarks about the SHP race results despite his directional issues
Next would be combat speed~attack speed, and reaction speed
These are very important to a swordsman as they rely on precision
And yes I will admit that he seems slightly underrated
In my thread about Zoro’s position relative to Apoo; I posted the panels showing his attack before it was launched; Apoo and Drake were clashing->Apoo’s right tonfa vs Drake’s left
Then as we see Zoro behind them, they did have the time to clash again, as is seen when Zoro cuts Apoo’s left tonfa and Drake’s right arm strike fails
But the noteworthy takeaways here are that while their second clash happened in the time it took him to launch his attack; he travelled a larger distance and did so without them reacting
Say it was a 2v1, but if Zoro gets the chance to keen the stance, Apoo cannot defend(although that’s more so related to his defense being broken as well)
So I’d say Zoro averages out slightly above most high tiers in attack speed
Reaction speed seems average; he can combat all high tiers casually
He is not very focused on CoO nor does he need to know as far in advance that an attack is coming as he’s not like Katakuri and Luffy in that they avoid most attacks completely, while blocking with 3 weapons requires much less time and moving around