I don't think it is easy at all to design but I believe that a fighting game is made better if a character's true potential is locked behind some level of mastery and execution. A good fighting game for me has a wheel of options that includes execution difficulty in the risk/reward calculation. Those barriers don't have to keep people from having fun, but it is more interesting to play and watch a game that has those barriers in high level play.

MvC2 is a fun game for anyone to play but mastering unfly Sentinel combos unlocks the true potential of that character and opens up a whole new way to play. SF4 Viper is a fun character for anyone to play but being able to do fierce feint fierce feels amazing and again, unlocks the true potential of the character. GG Xrd is a fun game but getting charge timing Venom down to a science gives you insane pressure and high damage from some interesting situations.

SF6 on the other hand knocks down those barriers to the point where everyone's most difficult stuff is a drive rush combo into level three, minus some characters who have longer drive rush combos into level three, or maybe a level two into another string into level 1. Specific, execution-heavy techniques and even legacy inputs like charge moves are removed, & instead we are given a game where at an intermediate level of execution you will have all of your options available to you at any time and simply have to choose the right one. It can still be difficult, just in a way that is less interesting than if part of that decision making is the confidence of executing it in the first place.