I think that the 1HBH's biggest weaknesses are clear; it's harder to coach, it's worse for RoS, and it requires more coordination/athleticism. It also limits your potential options for rackets bc it's hard to get the type of racket head speed you need with larger head size/HH/extended rackets (idk how tf Gasquet does it lol

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Contrary to popular belief, I think the 1HBH works best on slower courts where you have more time to set it up. I see way more clay-courters from South America and Southern Europe with 1HBHs than HC players from America, the UK or anywhere in Northern or Central Europe. Other than Fed and Shapo, the players with the best 1HBHs are strongest on clay. Gasquet, Stan, and Thiem are prime examples of this. Even Tsitsipas, whose BH is his biggest weakness, can spin em back cross court comfortably on clay, where he looks pressed for time on fast hard courts and grass. And I don't think it's a coincidence that the first GenZ breakout star on tour with a 1HBH (Musetti) is a clay-courter either.
IME my 1HBH is way more effective on slower courts where the extra time to set up lets me produce more pace/spin variation. I like to push opponents back with deep, heavy topspin BHs to set up attackable short FHs/BHs. I can't do this as much on super-fast courts, where my BH becomes more inconsistent and more attackable and I have to slice more.
But if your 2HBH is bad/isn't natural, or the 1HBH is more natural, I think it's better to have at least a so-so 1HBH than a bad 2HBH because even though you can try to just shovel 2HBHs back or slice only, that only works up to a certain level/can stagnate your potential unless you're Berrettini, who has literally everything except a good BH. I've seen him hit 1HBHs in practice and the Ultimate Tennis Showdown exhibitions, and I think it's probably a more natural shot for him and if he would've trained it as a JR, it would probably be better than his 2HBH. I know for me personally, I wouldn't have progressed as much as I have if I'd stuck with my 2HBH. Sure, I lost out in the short term a bit (high school) but in the long run the switch paid off.
This is the biggest problem with the 2HBH IMO. It can look technically sound (mine did) yet feel awkward and be garbage if you haven't had the mechanics/technique/cross-dominance* required for an effective 2HBH drilled into you from the time you were a toddler. That last one is important because a 2HBH is a non-dominant FH with your other (bottom/dominant) arm going along for the ride. My 2HBH sucked because I was hitting a left-arm dominant 1HBH w/ my right arm awkwardly limiting my range of motion, and I didn't learn this until well after I switched to a 1HBH.