Actually it would be good to have MLP in the 40k universe. They can be used as a legit excuse to have loyalists and traitors band together against a common threat.
holy emperor imagine if tiranids eat some MLP.... the MLP genes will overrun the tiranids and.... and tiranids are replaced by a great devourer MLP race....
That is not magic, that is warp powers. Total difference, because it works by using your brain. And using your brain is not magic; because then also tactics would be magic.