You know, I seem to remember lots of ragers resisting my sleep spells. Way more than resisted kotegaeshi.

Spells and skills both "fail". They just have different styles of failure.

Another example is this.

What happens when you fail a sleep/blindness/curse/faerie fire etc spell on someone (lose concentration). Or even if you succeed (ignoring sleep). You get hit with counterattacks. Does that happen when your dirt kick misses? I think not.

You are comparing apples and oranges and coming to the conclusion that because oranges have thick peels that apples should too, imho, without taking account of the fact that there are other pros and cons to each.