Well, i gues you are right ... Still think this matter should be adressed in tutorial so new players are informed well.
As for Paladin ... i can imagine it goes frustrating. But i believe in this particular case (since feel free to corect me but i think Smite is not a reaction) it would cause not colision, if set on auto against stronger enemies so you dont have to re-confrim it for every single swing.
In the words of the senior NCO instructor at cadet battalion: “If you ain’t cheating you ain’t trying. And if you got caught you didn’t try hard enough!”