Issho has a massive matchup advantage against a flying speedster like King since he can nope his entire fighting style.
I wouldn't actually argue that King would win a fight with Issho. However:
- A heavily nerfed Dressrosa Zoro could push Issho back with a single sword.
- Rooftop Zoro was sent flying by Base King even when blocking with 3 swords.
Issho can't treat Zoro the way King is currently treating him.
King abandoned his fighting style to face Zoro at Zoro's own specialty and bested him at it.
The last time a character was disrespected so badly was Sanji and Vergo.