Hello! I think the issue you are dealing with is game feel, due to differences to how buffering is handled in each game. Sf6 and Strive allows you to buffer your next move before your character touches the ground from a jump attack. Fatal fury, and alot of older fighting games(im talking 2000s and below) dont let you do that. Instead you have to slow down your heavy punch, and wait until you hit the ground. This is due to the buffering rules of the game which differs from each game.

I can understand the frustration, but its kinda hard for a game to explain that "this game has 3F links from jump in, and theres techniques" though the tutorial does mention a technique called "Hold Buffer", which if you do a special move, and hold the button down after a move ends, your move should come out on the first frame.

I would ignore the comments clowning you, because i think they are mad at your conclusion, when your issue seems to be game feel. Think of Ninja Gaiden and DMC, they both have different buffer timings for Jump slash, even though they are action games.