The problem with those mow charts is that is under perfect/ideal conditions.
Example, my Huster Super Z zero turn is 35HP with 72" deck.
Top mow speed is 14 mph. They claim that mower with a similar chart can mow 8.14 acres per hour.
If you can mow 14 mph without ever slowing for any turns, without ever slowing for trees, buildings or bumps. Full speed 14 mph flat out for 1 hours/ perfect conditions I suppose its possible.
Now throw in trees to mow around, bumpy areas, driveways, buildings, Etc. the best I've been able to do with that mower mowing as fast as I can on our property is 4 acres per hour or a bit under.
My average on the same property with the tractor and an 84" rear finish mower is around 2 1/2 acres per hour.