Imu's sword attacks are below Mihawk's because of his title as the WSS, which is true both in name and in actuality.
That's the conclusion we should draw from this. Based on Imu's feats, we can see that he was able to take out either Luffy or Loki with sword attacks alone, which only upscales Mihawk even further.
As for Imu being a swordsman, I don't think he is. He's more like Daz Bones:
someone who uses a sword alongside other bladed weapons.
" Don't go calling me a swordsman.
As long as it's a
weapon capable of slashing apart (bladed weapons) the human body...
that's enough. "
He uses both a sword and a spear.
So people can call him a swordsman because he uses a sword and other bladed weapons, just as they could call him a spearman because he uses a spear and other bladed weapons. He isn't exclusively defined by either weapon.
This is about Mihawk's title and whether Imu is a swordsman.
As for EoS Zoro, he isn't affected by that, since he defeated Daz Bones, who fought similarly to Imu, and has also defeated numerous swordsmen.
So EoS Zoro's strength isn't limited by Imu.