"That's a Debian bug" is not useful - you can only determine that after you have analyzed the bug thoroughly, and gone to the length of getting out a Debian system instead of whatever you're usually developing on.
But yes, some maintainers are very good and some are quite bad; however, Debian's policies and patch-happiness means that bad maintainers (can/tend to) do much more damage than in other distributions/OSes.
Well if you really want to play tough about it you just say that all bug reports for your software running on Debian must go through the package maintainer. You could even ignore them if you get a lot of bogus ones.
Yes, but even that is a half-solution - Debian users are still likely to think you suck and/or use alternatives, which means less users/prospective developers/testing.
But yes, some maintainers are very good and some are quite bad; however, Debian's policies and patch-happiness means that bad maintainers (can/tend to) do much more damage than in other distributions/OSes.