I really don't think he has major balance issues the larger HP pool goes a long way and his tools have enough upside. I think he bullies up close, his great d4 keeps him poking, his health balances out his slower projectiles which are pretty good when you get them going. A great armor move. Kameos help patch up the holes. You have to play kind of lame sometimes but he has this explosive potential and I like pressing buttons with him.
But I agree there's a level of frustration that comes with him, not in his animations or characterization in my view but in his hit reactions and the way his kit gels together. He reminds me of Rambo from MK11, where stuff seems tougher to land than you would want, certain moves have these janky hit reactions, some inconsistencies across characters. Given that he was the 'secret' unlockable character, I wonder if he was actually gonna be the boss or something and was a late addition to the roster, and came out unpolished partly because of it, but that's just a mk theory. Again I think he's quite fun, but could use some love.
Like having better launches off of NeoPlasm and Blood Ball, better frames or recovery on S3/S4, that F13 string or his F122 having more generous ambush launches. Give him more active frames on something to meaty with.
At any rate, I've been liking Tremor with him. He can take advantage of basically every ambush Tremor has to offer, the projectiles are a nice touch as always and he lets you do cheap stuff if the opponent turtles for some reason. You could just go with the armor the whole time, you can setup the overhead/low kind of off screen after a BNB into DB4 knockdown, you can do a ton of chip and be safe of EX DB4, combo into life thread from the B22~throw, make anything safe basically. (Does he have a back throw combo?) Even the simple variation switch is a nice way for Havik to get his projectiles going. Typical Tremor stuff but he just feels useful for Havik, you can really just turn your brain off just ambush into the next thing. You also get that extra 100 HP, those long Tremor cooldowns wont feel as bad when you have a 1200 HP to turtle around with.