While i don't know the specifics of the situation you encountered, a common view (not the only view) is priority should be set by people who are going to do the work to fix the bug (or in consultation with them), except for "unbreak now". This may or may not be WMF staff.
The problem is that almost every bug is important to someone, so if everybody sets priorities just for the things they care about (and people tend to only increase them never decrease) every single bug ends up being set as "high", even the ones that people generally think are useless and noone intends to work on. The end result is the priority field becomes ignored, because it no longer reflects the real priority of the bug.
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