I learned this about United this summer. Except the language they used didn’t specifically rule out roller bags, it called them “full-sized carryon”. I showed up with a checked bag and a small carryon. The desk agent told me wheels make it a “full-sized” regardless of the dimensions. Fortunately, I was able to stuff a bunch of stuff a bunch of my crap into my checked SCUBA bag, and repack my regs and underwear into the backpack I was bringing anyways.
Note: This was on an International flight so I REALLY didn’t appreciate feeling like I was flying on a budget airline.
Lol, Hilarious and justified but I get quite compliant around people who could stand between me and a SCUBA/ bachelor party trip.