A bunch of my neighbors have professional lawn services, and they all come with high-end zero turns (of one kind or another; can't read them even with binoculars). Of course these are pretty flat suburban yards, not woods. They all go pretty fast. I once timed them doing roughly the same corner-lot
front yard as mine, and they were done in about 4 minutes (never bagging, just mulching). And they come like every ten days-two weeks, and mow whether it needs it or not. With my Honda self propelled walk behind (only mowing when necessary), always going deliberately slow, and dumping my bag when half full multiple times, it takes me about 30-40 minutes.
But these guys obviously have lots of practice (it shows), and their decks are twice or more my 21 inches.
If I had one of those zero turns, I'd probably put my new truck on the street first so I didn't ram into it by accident.

Preparing for 24 hrs of rain here. Just mowed yesterday. Praying over my sump pump shortly.