Well, first, we've not actually been discussing any specifics about arbitration. The most specific we've been is acknowledging that arbitration is a point of failure, and that police unions are involved in negotiating over the arbitration framework. Neither of those things points explicitly to police unions as a point of blame. For example, arbitration problems often stem from lack of evidence, lack of consistency in application, and lack of increased punishment for repeat problem officers; none of these problems are directly related to the contracts negotiated by police unions (obviously they are indirectly related). Blaming police unions, simply because they represent officers, which is their mandate, is an oversimplification.
Additionally, systems like arbitration, or the arbitration framework contract negotiation, is predicated on the idea that both interested parties represent their position adequately, in good faith, and without conflict of interests (among other things); this is not always the case, but is the side that is representing their position adequately and in good faith (i.e. police unions, making it harder to fire "good" officers) to blame? Another example, in other terms, many people are punished unnecessarily by judicial systems because of inadequate defense (i.e. ineffective assistance of counsel), but is the prosecutor always to blame?
It's not that other parties are necessarily at fault for failing in negotiation, but that assumes that those parties adequately represented their interests (in this case, one of those interests would be the public interest), which is certainly not a given.
> I am not claiming that unions are a net detriment to police union workers, simply that there are tradeoffs.
With this in mind, I guess I should've rephrased my initial question. I should've said "can you provide some insight into how police unions work poorly for police officers generally (i.e. their members)?" Obviously there are cases where police unions (and other unions) work poorly for individuals, but I meant where they work poorly for their members overall. This is why I think your reply fails to fit my intended framing and I was rejecting the premise from that perspective.