Camrac, to answer your question, here is why i think his learning curve is high.
-Ermac old school bnbs are easy as shit. All of his best high damage combos require some extent of execution. Depending on the combo, whether it is off a string, naked lift or an AA, you need to ( on the spot) react to which combo you are to be doing. Also depending on the character you are playing against, whether or not to end the combo with double jk or f4. Now im not saying this is impossible to do, im just saying that there is a lot of thought behind his combos and this is not something you pick up on right away. Also people need to learn double jk combos.
- Understanding how tkp works. Most of the ermacs ( all except metzos,myself and a few others) don't use this move the way it is supposed to be used. Its not like a projectile, it controls space. Try and think of it as a much more punishable d4.
-Walking. No one walks. I see metzos walk, and if you have seen me play, all I do is walk. Walking all the time, in every situation and staying calm is not something people do.
-Patience. With a lot of characters, there is always something you can be or should be doing to make your opponent react and do something. With ermac, i honestly believe patience is important. more then half of my won matches is from punishes and just walking back and forth not doing a thing.
-learning how to use his tools. Iafb, u4, d4, d3, d1, tkp, f4....etc etc etc
Ermac has a move for every situation and because of this it can be hard at times choosing the right one to get you out of a situation.
Knowing when to use his moves is what makes him good. Sure f2 and sweep are frame traps, but when people start getting caught by naked lifts after those traps I see a lot of ermacs failing to decide what to do and how to apply pressure. Learning how to keep his pressure going to vital.
-Non combo execution.
iafb is a bitch to learn to do in every situation that you want to use it in. most of his block strings end differently frame wise and this means adjusting to get iafb as low as possible.
his b2 cancels are execution heavy when you are using them often enough and creating set ups with them.
-reading people.
the majority of ermac damage comes from reads. he has no easy way in. its all spacing, zoning and reading.
and reading someone is not something you can teach, this is something the player has to learn. Because there are a lot of brainless ways to play other characters, playing brainless ermac gets you dead and fast. So adapting and reading are important parts of his game. More so in my opinion then other characters.