Mecha Kha also doesn't have a completely new voice over(that includes 2 VA) or a complete new set of animations.
So no it is not on par with PFE,not even close.
And in general,this is because kha has such a complex base.
Every skin of him will have an evolving model,which is something that is normally only used for ultimate skins,simply because that is part of kha'zix.
And if we look at PFE and compare it to every other legendary,then it has objectively more features than any legendary skin,since it gives a new model,new VO,new Animations,new Spell effects and has an evolving model,whereas almost every legendary skin only has the first 4 things(the only ones with anything additional are DS thresh who has a lantern that changes form at one point and Project ashe,who gets her hood in certain parts of the map,but both are less than PFEs model changes)
So it still has more than any legendary skin.