My understanding is that all characters have access to the same principles, but they have different strengths that lead to different playstyles.
So for example both Sagat and Ibuki can play a really defensive style, throwing projectiles and zoning the opponent, but ibuki has really awful damage from her normals (One Sagat kick deals twice as much damage as Ibuki's), so Ibuki instead relies on dealing her damage through mixups on the opponent's wake up.
She still has to go through the same neutral game as Sagat, it's just that she won't be dealing any damage at this stage in the match.
You wouldn't expect to notice any difference between characters without knowing these "stages" of the game, and commentators do an awful job at explaining them because they're commentating to experienced players, as this game's community is 10+ years old.
You know how SSBM has a shit platform? E.g. no matchmaking, requires mods and emulators to play, no support from developers? Fighting games have been improving a lot in this regard, and arcade stick are one of the things that probably won't be necessary in upcoming games.
Like, it's not required to use an arcade stick/hitbox to perform well, but it feels like you have to go MacGyver on your PS/X360 gamepad to do some special moves, because the game was planned around arcade sticks. This genre suffers a lot from internet lag, you'll be playing a lot of tournaments on LAN, so expect even more MacGyver if you get used to, say, an X360 controller and have to buy an adapter to play on PS4 or something.
You'll have to learn all inputs from scratch either way, so I would say get a PS4/PC stick (no SF5 for xbox, so xbox is kill) only if you plan on playing fighting games for the next 5 years.