As others have said, don’t take much notice of the ethnicity percentages.
In defence of My Heritage, I have found some very good matches, including a few from my English/Irish side.
Ancestry hasn’t been as useful for me, and since I haven’t renewed my subscription I now can’t see anyone’s Ancestry trees. (I was aware that this would be the case)
I guess there is some luck involved.
Just to add: recent contact with a not particularly close match on MH has led to reuniting two branches of a family in different continents which had lost contact in the 1920s.