If you're getting matched with players of a lower elo than you it is because your hidden RR is likely lower than your actual rank. Either that or the diamonds you are playing against have a very high hidden RR (maybe they haven't played so much this Act, etc). So actually, based on match wins and individual performances in those wins (elo), they are the same as you.
I'm not suggesting you don't have a better understanding of the game than them as you claim, but if you want to play against Immortals you need to improve your win rate. As much as it is convenient to just claim the game randomly matches you against lower elo players just because, it doesnt... that's copium.
Anyway, I agree with others here that if you ain't feeling, don't play. If you change your mind and wanna duo with a decent player, lmk :)