Hey the answer to this question is whatever you want to do is ok. Playing guitar is a perfect example of you get out of it what you put into it. I know from experience that the pinkie is weak but like everything it can be strengthened in a relatively short period of time.
Do the spider exercises with all 4 fingers up and down the fretboard and you will soon find out you can play that Power chord with all the fingers in the best place. Its a boring drill but I think the single best drill for strengthening and improving accuracy.
Playing the chord the way you suggest is not wrong its just not right.