Horsepower is not the only measure of a machine's quality. Wheels, cables, controls, handles, etc. They are all part of the machine and are typically much better on the commercial machines.
Commercial 21's aren't trying to compete with Murray or Yardman with their bargain basement Tecumsehs or Briggs. I personally owned a Honda with the 5.0 horse OHV--NOT OHC--engine--the "good" one. I don't know if deck design was a major factor or not, but I can say for sure that my boss's old Proline with the 4.5 Suzuki would eat the Honda for breakfast. I also have an early 90's Deere with a 4.5 Kawasaki. This is also much more powerful than the Honda could ever dream of being. My buddy's dad just picked up one of those new homeowner Toros. It's got a 6.75 Tecumseh. Guess what, it will bog down in grass that my 10 year old Kawi will plow right thru. Just goes to show you that manufacturer's claims of horsepower ratings don't mean much.
As far as Lawn-Boy being the best 21" out there, I will have to respectfully disagree. The commercial machines might not be too bad, but the homeowner models are pretty chinsy compared to any Honda, Deere, or good Toro that I've compared them to. They do have decent engines and a good flowing deck design, but the handles and decks (steel) are pretty darn flimsy.
IMO, Lawn-Boy's last good 21" was the Gold Series w/ 3-speed drive, last made in about 1996. And Toros were the Super Recyclers w/3 speed drive, also last produced around '96. Both these machines had aluminum decks and sturdy handles, etc. A far cry from the new Personal Pace models.
Anyway, to make a long story short, go with a ProLine 21" and don't look back! Seems like everybody forgets that, yeah, while you can get 5 Murrays for the price of one Toro, all that time you are using a POS that is making your job harder.