I think that making all slides go under projectiles might be a little too much, especially for a grappler, even one as limited as Hakan
I think the best route would be to have only Lp slide avoid projectiles. Since it already kinda does that, the idea wouldn’t be seen as unfounded as across the board projectile avoidance. to further keep the move balanced, I think that fireballs that hit twice like most EX fireballs should be able hit hakan, so projectile don’t become a moot point against Hakan.
with a projectile proof LP slide, hakan’s mid-range game will improve I believe. Right now, when hakan is about half-screen away from the opponent and to far away to use his pokes, trying to sneak around or under projectiles can be tougher than full screen since there’s less reaction time, and the current LP slide needs really good timing to dodge projectiles. An improved slide will allow him to punish more in that close-to-middle ranged game, so that would also serve the purpose of making him scarier to approach.
such a change isn’t too broken of gamechanging either, since it wouldn’t allow for fullscreen projectile punishment, just a way to get hakan closer. It would still be risky to use it, due to the slide’s massive recovery when wiffed, but it can still give Hakan-users a little more to work with.
as an example: Ryu throws a hadouken from full screen. You do a Lp slide nice and early, and even though you’re nowhere near hitting Ryu with it, the slide lands you practically on his doorstep. Or if Ryu throws one from half screen, you can throw out that slide to punish it without having to worry about timing it as precisely as you would right now.
that’s just my 2 cents