Ok, I know I have written about Hayato several times in the past, however I really, really believe he's rather underpowered. He is, in essence, a fast-paced mobbing warrior. His 1v1 skill, Maplestory mobile mesos, seems fairly underwhelming, even with Hypers believed and even a decent piece of funds. 

Specifically, he's got no bind, silence/seal, or the like to counter things like Damage Reflect and Cancel Physical Damage. This endangers him at worst, hinders him at least for many major directors (Empress, Hard Magnus, to mention two ).

Besides that, I believe that Hayato, for it is current underpowered status, is rather hard to buff with out becoming overpowered. It is already kind of a bully class early to mid game (Lv. 30-130) in terms KSing possible for his or her mobbing abilities, plus his blisteringly fast attacks. 

If you were to correct the harm%'s of buy MaplestoryM Mesos his Sanrenzan, or perhaps add extra attack lines, it gets him overpowered. Maybe if Shinsoku needed a higher% damage per line, it can help things, but I'd suggest including a dab of some sort to his kit.

Now, abilities aside, I believe that there is an even greater reason he doesn't get as much love from gamers: his command. Granted, he has 60% command from the very beginning, but that would be it. Other classes get 80% control, maintaining their harm relatively steady. Hayato? His harm jumps about as far as he does. There's also the issue of his attack multiplier (which is quite hard to adapt in a way that's balanced).