every time an update is tested against this filter, a Client.get_chat_member() request is executed. This is a network-bound implicit behavior that might result in unexpected results (eg. being rate-limited by the server), I believe it should be up to the developer whether to use (and how to implement) such filters

every time an update is tested against this filter, a Client.get_chat_member() request is executed

Yes, but this is the only way to know that the user is an administrator, as I know. If someone wants to check the admin, they still have to repeat it, and this, it seems to me, is not a rare use case, therefore it can be useful as a standard filter.

But if this is really such a bad practice, then I am by no means insisting.

Honestly I doubt this is of any usefulness. Most use cases for this are when writing chat manager bots, which need specific behavior tuned for their use case. A generic filter is rarely useful