All the grooves in the game CAN be played scrubby. If you’re going to compare them in any way, you have to look at what the grooves have to offer, and what the person has to learn in order to play it.
I put K as the most scrubbiest. This does NOT mean it is the worst groove. All it means is that the person playing K has to think about a lot less. The game/their opponent will do a LOT of the work for them. So a person not really knowing the game will still get a level 3 pretty easily, and then it’s just one lucky super. The “building your meter” aspect of the game is pretty much thrown out the window. GOOD players help themselves along by JDing and taking safe hits here and there. However, giving yourself extra damage and level 3s is a no-brainer in K, hence it is the most scrubby.
C is probably the next scrubby. Anyone familiar with the Alpha series can usually do well with only a few minor adjustments. After learning about lvl 2 cancels, they can easily get into the flow of things, as C didn’t gain much else to separate it from the Capcom Groove of CvS1 (and consequently Aism in A3/A2 without CCs). While there are some advanced things about C (late airblock, lvl 2 cancels that lead to meter instead of direct damage, etc.), it’s pretty straightforward.
P is next because the groove has very little to offer in the first place. It has parry, delayed get-up, dash, and low jump. A 3S player can usually adjust to the different parry timing fairly quickly, and they just have to learn how to use the other 3 options. They don’t have to care if a move is being RCd or not, as parry will take care of it either way. P may stand for patience, but it’s not really about learning different actions for different situations. It takes skill to WIN with it, but not skill to LEARN it.
For the same reasons as P, S is next. S is so limited to begin with, it’s pretty easy to learn what the groove can do. As with P, once you learn its options, then you have to add patience to the mix.
I think A and N are tied for least scrubby. As with all grooves, they can be played extremely scrubby (Roll CC for A and activate-immediate level 3/Roll Level 3 for N), but there are more things that are situation specific in A and N. In A you need to know Anti-Air and Ground CCs… then you need to learn how to do Combo into CC… and then there’s the setups for their poke so you can Counter CC… lots of little things that take time to learn how to implement correctly - and that’s saying nothing of learning the actual timing of certain CCs.
N just has so many options, it takes more time to understand it. It has run, low jump, AND RCs (the only groove with all 3). It also has counter roll to help cover up characters’ flaws (inability to counter blocked Blanka Ball, inability to AC things like Sakura’s CC, not being able to retaliate against certain combos, etc.). The solutions are there for N-Groove players… they just have to learn them. And learning all of them takes a lot longer than for most grooves.