The Deep Sea King was a very powerful One Punch villain who was able to go up against Genos, Sonic, and several other fighters in back to back battles. That’s a very impressive thing to do but Genos has gotten way more powerful since then. I don’t doubt that he would be able to very quickly take this guy out. One or two incineration cannons should do the trick and the king isn’t quick enough to catch him. Genos wins.
Suggested by Destroyer The Ancient King never got to do a whole lot since Tatsumaki took him down in an instant but presumably he can hold his own with any of the other kings. That’s the kind of ability he’s got but there’s no chance of victory for him. At the end of the day feats are what really counts and Deep Sea King was able to go up against guys like Genos and Sonic. Deep Sea King wins.