Most warrant officers I worked with had been NCOs of the E6-E7 flavor before going warrant.
I was also lucky to serve under several mustangs, one of which was a former E7*. Another musting I knew as an E7 who was the platoon sgt, got his commission, and came back as the platoon leader O1. He may have been a 2LT, but he was no butter bar.
* Also served with an E6 who had been RIFfed when he was a company commander O3 some years back.