Normal seems pretty easy.

I beat wol campaign at normal, but it says I'm 40%.

pretty easy, but u'll have to restart here and there at some mission.

Brutal is still difficult, but noticeably easier than WoL's Brutal. You should have no problem if you're macro is decent and would probably only need to reload every now and then in case you get into a bad engagement or get caught unprepared for something.

It's easy, I think WoL, even on hard was more difficult.

Its easy. Build mutas and steamroll.

this + kerrigans hp/damage buff!!

Kerrigans best spell is actually the spawn banelings

Jim raynor spawns banes on kerrigan in a cutscene missing from the campaign.

It's not that hard, Kerrigan is so OP in the game, she's really all you need.

It's easy peasy.