That is why some of the more expensive ones have their own pto driven pumps and have a minimum HP rating. Just not enough flow their on most for larger cylinders. Equipment has changed a lot over the years and more stuff is being run with hydraulics so pump demand keeps rising to that extent.
I actually like my 3 pt splitter. It has a PTO pump. Hours on the tractor arnt a issue for me, i got the tractor to use it. It will split horizontal or vertical. One less crappy gas engine i have to take care of lol.