It’s difficult because you’re adding another set of outcomes to any situation, and you have to be ready for it. It’s not braindead.
Applying it to your counterpoking game is the first step, and perhaps the easiest as Fei’s cr.MP is too good. You can just spam it and correctly whiff punishing it is hard, and by that I mean reacting to the whiff and not just pressing a button and passing it off as one. You have to be ready for:
A) Did it hit? - Nice!
B) Did it counterhit? - Confirm into cr.HP/Rekka.
C) Did it whiff? - What did the opponent do?
The fact that there is a third outcome and that your POS could potentially come out mean you will always have that in the back of your mind as a potential outcome if they mistime a whiff punish. If you just whiff normally, you’d just expect either to be whiff punished or not whiff punished. On top of this, you also gather information on whether you can or can’t get away with using it freely depending on whether you are punished on the whiff. And for anyone that’s fought players that use it, you have to be ready for them to bait out the POS.
It adds another element to the game at the very least, and one a lot of players will consider bullshit until they understand how it works or the repercussions of it’s misuse.
Combine this with the rest of what you’re already concentrating on in neutral, as well as any character matchup knowledge you need to apply, AND player knowledge that you have to apply then and there - it’s not easy at all.
But that’s only one element of it.
Using POS as part of Okizeme and in blockstrings is the next part, and provides a whole new set of outcomes that you would need to be ready for. Using it on the opponent’s wakeup means you’re forgoing any other safe Oki you could have used in place of it. You also have to be ready for the OS not to activate, and be able to keep the pressure on, whilst inputting the POS correctly in the first place.
In blockstrings, you have to be aware of the correct strings to use on a per character basis. You need to know, that after a certain string, which of the opponent’s options are completely stuffed by the POS. Which button is the opponent likely to hit after this string? What is their best/safest option? The opponent could just do nothing, and you again have to be ready for that while at all times inputting the POS correctly on the normal you ended your string with. They could have been hit by your string, so then you have to change it on the fly to convert damage.
Then there’s working it into your CH/Throw game…
There’s a lot more to it than it just being a system quirk.