Right, and that's essentially what this comes down to. In reality, it shouldn't matter if an umpire makes 10 errors spread evenly across two sides or 10 errors all favouring one team. It might, in a sense, be better for the balance of the contest if they were more evenly spread, but it certainly doesn't reflect in any meaningful way on their capacity as an umpire. A mistake is a mistake and naturally the victim of it is going to be essentially random.
The only reason it would matter if all those umpiring errors went against one team would be if there was reason to believe they were not in fact errors, which is obviously a totally different accusation from one of incompetence.
I don't object at all to Bucknor being removed from the elite panel if it is deemed by the powers that be that his abilities are no longer good enough, but it is somewhat distasteful that a veteran umpire of over 100 tests who has many plenty of mistakes in the past (as all umpires do) was last week considered capable by the ICC but is no longer, because of the protest of one particular cricketing body about one series of errors that happened to go mainly against one side. If Australia had copped half a dozen bad decisions and India only a couple, would the BCCI have lobbied for Bucknor's removal? I think the answer to that question is obvious, and in that case he'd probably still be umpiring in Perth for the third test, and that's the problem here.