I saw someone saying that if you get good at SF4 it'll hurt you in SFV.
I think that's a lot of horseshit and not at all true. Look at someone like Arturo who doesn't really use alot of the bullshit found within SF4 and still places well. If you develop a strong game that doesn't depend on option selects within one title, those skills will translate to other games as well. It's great to understand and take advantage of what's within the systems of a game, but if you're just trying to start with fighting games then you'll have to be willing to let your first serious title be one that you develop organically within.
Like with SF4, at this point there's no real reason to try to become the absolute best tournament winning player at this stage, especially if you're new to the genre. Learning option selects and various other system exploits may get you some quick wins but those don't translate necessarily. Furthermore if you're just using an option select but not understanding when to use it, you'll just lose anyways.
That said if someone learns how spacing, whiff punishing, anti-airing, dealing with pressure on wake up etc in a pure sense, it really doesn't matter which game you're learning. You just need to be willing to be patient and let each aspect of a game develop as you grow to understand it.
The frame data in SF4 won't be the same as SF5 or it might not work the same in MKX but once you are able to develop an understanding of what frame data is with something to reference, you'll be able to understand how it differs in another title.
Understanding why option selects work and how they work is probably more important than learning specific option selects when you're first starting out. If you do that then you'll be able to even discover your own in new titles. You just need to take the time to understand how the games work before really going too deep in.
Kinda rambling and I probably offered nothing, but I just didn't want someone to think that learning SF4 now will hurt you in SF5. It's not what you learn but how you learn that matters in the formative stages.