Trying to compare the powerjack and the escape plan is really an apples vs... well ok maybe not oranges but definitely at least like pears or something.
An escape plan solly at full speed goes faster than a powerjack pyro. Yes, the pyro can go faster at other speeds, but then the soldier has an advantage that the pyro doesn't have - he probably has enough health to rocket jump and increase his mobility both vertically and horizontally. Notably, the pyro can never improve his vertical mobility, and RJing is still way, way faster than escape plan. Pyro can never have the mobility that soldier provides, you're comparing two unlocks but not looking at the class as a whole.
Besides why are you complaining about an honestly pretty well balanced weapon like the powerjack when you could spend more time worrying about the rest of the valid points in your post because I'll admit I consciously abuse the fuck out of everything at my disposal on the class and I can tell you there's a lot wrong with it