Motion inputs aren't arbitrarily difficult. They're intrinsically tied to the game's balance. Basic special uppercut moves like the Shoryuken use the forward->down->downforward motion to ensure the player cannot hold back to block during the motion. The player must commit to use their strong special uppercut move frames before they've actually unleashed it. Guile's Sonic Boom projectile requires the player to "charge" the move by holding back for a couple of seconds before being able to unleash it. This creates a risk factor, since the opponent is then incentivized to cross up Guile to make him lose his charge. However, this is where Guile's special uppercut, the Flash Kick, comes into play. The Flash Kick can be simultaneously charged along with the Sonic Boom, to disincentivize the opponent from attempting to jump over Guile. Mapping any of these moves to a single button press is a balancing nightmare. Street Fighter 6 has a "Modern" controls option that does exactly this, and it comes at the cost of a big chunk of the character's available movelist. Even with that huge tradeoff, the Modern versions of several characters are still considered high tier. Even then, you hardly see any Modern control players in the upper echelons of Ranked matchmaking because, ultimately, it's way easier to learn the motion inputs than it is to have a solid gameplan.
Street fighter isn't bad at all but some games and some characters are just absurd for no particular reason. Ivy in later Soul Calibur games is a good example, she has two command throws with pointlessly arcane inputs that even have a second, better mode when you do them frame perfect. So everyone who plays Ivy just grinds and grinds until they can do it in their sleep. There's no particular balance reason for that (also Soul Calibur has a block button so the usual balance rules don't apply), it's just a "you must be this tall to play this character" barrier.
You just said yourself that doing them frame perfect yields a better version of the move. The input is difficult because of the potential reward. It's like doing perfect EWGFs in Tekken. I played Ivy in SoulCalibur II, and could do the Summon Suffering input pretty consistently if I buffered it during another attack. It led to a fun mixup since the other player would hear my joystick switches actuating as I did the motion, and crouch to avoid the throw. Instead of finishing the input, I'd hit them with her 2 A+B overhead instead. God, I love SCII. It's a shame the sequels kept trying to reinvent the wheel with the gameplay.
> You just said yourself that doing them frame perfect yields a better version of the move. The input is difficult because of the potential reward.
I also said the other half of that: that the result is that people grind until they can do it 100% in their sleep, and thus all it forms is a "you must be this tall to play this character" barrier.
Unlike the example in Street Fighter it actively works against having a balanced game, since now you have to nerf the move because the people who ground it frame-perfect are too strong, which wouldn't have affected anyone who didn't stick their nose to the grindstone but now they get to eat the nerf too, so the character ends up about level with other characters when you're frame-perfect, which isn't demanded of other characters. We saw this exact antipattern happen with Ivy in Soul Calibur 6.
There's an argument to be made that the arcane input provides a tell to the opponent when it's used outside of a buffered section in some other move's lag, but that same argument would work with a less pointlessly arcane input, like a double half circle.
I don't get what you mean by "you must be this tall to play this character". Equating height to skill is a false equivalency. You can't get taller by practicing. Either way, it sounds like the devs just messed up the initial balance. It ain't the fault of the players who were serious about learning the character. That's the modern conundrum of games in the post SFIV era; constant balance patches before the full meta has been explored. Personally, I'm often dissuaded from trying to learn top tier characters in new games because of the fear that all the muscle memory I build will be useless when the game gets patched. It's gonna be interesting when Street Fighter 6 gets its first big balance patch a year in, and all the Ken and JP players take to their keyboards to complain.
Conversely, characters like Carl Clover in BlazBlue. The difficulty of controlling 2 characters seperately but in tandem is challenging but not difficult to input inherently.
Once you get used to the input style the complexity makes the character and thus the game more fun and interesting.
