Thief main since beta, if that is important.
PW is not unbalanced it mirrors other chained sword skills of other professions (blurred frenzy, hundered blades e.g.).
Like all sword and greatsword melee builds S/x on thieves relies on the “extreme” range of the cleave cone and the disproportional high base damage on all sword attacks, pistol wip is the culmination of that.
Generally sword damage is to high on all proffesions given that it has a AoE cone of great range, compare this to dagger damage which is single target and does not cleave and has less range.
In sPvP this makes S/x for thieves superior since by the nature of the conquest mode everything and everyone is usually stacked up on the point.
The thief is defined by being able to repeatedly use the same move PW evades are the only option thieves have to stay on the same spot for several seconds without getting shred to bits in seconds or being cc’d into oblivion thieves have no stability and no protection to passively achiv that goal so they need the active version the evades provide, this is what makes PW strong in sPvP since that mode is all about staying on the point and area denial (here done by AoE cleave damage and evades).
PW forces your opponent to move away if you can not you get punished hard, there are lots of options for other proffessions to do that way better therefore PW is balanced. People complain about it because they are not used to it and not used to being forced to move away from a thief nor to thieves being able to stay on point like almost any other proffesion.
On a personal side note: I do not belive that S/P warrants the attention it gets at the moment it only makes the thief an “inferior” version of a warrior.