It's important to focus on what YOU can control. So many things in poker and MOBA games are out of your control. It's hard enough to play perfectly in both of those games, and even harder to comment on your teammates/opponents play and still keep playing perfect yourself.
I like to think of poker rage/MOBA rage as the same thing as road rage. I have friends who are very smart people, but put them behind the wheel of a car and EVERY other driver is a "****ing idiot mouth breather who can't tie their own laces". For whatever reason, road rage never bothered me. I saw it as a series of dynamic decisions that I had to make based on my surroundings and other drivers in order to get to my destination safely (sound like poker and MOBA games?).
But take me playing poker or a MOBA (Dota2/HoN specifically), I was a little nugget of rage. Every one of my teammates/opponents were ****ing mouth breathing idiots who couldn't count to 5. Anything would set me off, a small suckout, a teammate being a little out of position. I don't know why there was such a difference in terms of rage behind the computer vs behind the wheel for me, because I think they're both fairly similar.
I'd like to think I've gotten a lot better about it these days. Making the analogy between road rage and poker/MOBA rage kind of helped put things in perspective for me, and I can confidently say that I'm not nearly as ragey/tilty as I was a few months or years ago. As a result neither are as stressful