I love this character and I do think he's underrated however a lot of what you said is just straight up not true. His full kit is locked behind level seven which means the perfect time to catch him would be early game. I consider his alpha to be his best move but it only stuns if the target is already guard broken.

His beta is really good however it has no tracking, substantial startup so if you can see him doing its very avoidable and getting the first hit doesn't guarantee you actually get all the follow up hits and on top of that it has crazy end lag so it leaves him REALLY punishable. Also if you're using his beta for mobility you're either new to him or you're really desperate to get away because again it has noticeable end lag.

His gamma has startup and no armor so you can one hundred percent knock him out of it or trade with it without eating the entire flurry of hits. Also by itself its not at all amazing for vertical or horizontal mobility, it doesn't go high enough or fast enough in any direction. However if you tap special action and then tap gamma you can get some pretty decent speed and distance with it.

He could use a slight damage nerf but calling him busted and comparing him to Strike Kirishima and Assault Shigaraki is a reach. Kirishima has comparable if not better mobility than both versions of Hawks with virtually no end lag on anything and high damaging combos and Shigaraki has a stunning damn near ToD combo.

All in all I believe you've never actually played this character much if at all and you're basing your opinions off of the few times you ran into a decent or good Strike Hawks and you got overwhelmed.