Use a roof mounted 10-20M ground plane where the vertical polarization can be useful; many AMers get nosebleeds on those bands.
Verticals on the higher HF bands stink unless you are trying to work the occasional stuff overseas. That probably explains why after all these years I've never heard you on the air before. I've used verticals on 20 thru 10-meters before and they were awful for working AM here in the U.S. I've also used 80-meter coax fed dipoles on 10-meters and 40-meter coax fed dipoles on 15-meters, but the bandwidths were so narrow that if the transceiver didn't have a built in auto tuner to keep it's 50-ohm output happy it wasn't happy. And, trying to use them without a tuner on the tube stuff wasn't much better and you had to have one to try and bring the receive level back up when you moved too far away from it's resonate point.
Granted, a center-fed Zepp fed with OWL will leave a lot to be desired on the higher HF bands because of no gain, but at least they will work for someone who only has the room for one antenna and it will still work better than separate coax fed dipoles any day of the week.
Anyway, what works the best on the higher HF bands is a horizontal Yagi with at least 3 elements. 8dB to 9dB gain will do more good than anything. I still use my 10-meter mono band Yagi on the tower, but I'd like to have a tri-bander or one that even has 12 and 17-meters then use the my Zepp on 40-meters on down.
P.S. And yes, everyone uses the term "tuner" when the correct term is antenna coupler. It doesn't really tune the antenna, it simply matches and couples your source Z to it. Using the term 'tuner" is just a bad habit we have all falling into.