Priority definitions don't reflect reality

Please note the discussion about  QTBUG-61053, especially the response by Jake Petroules in the comments section of 5.9 release blog post.

Here is the argument from Jake Petroules about why a P0 issue's priority was lowered to P1 after 5.9 was released:

"Because Qt 5.9 has already been released. As such, by definition the issue is not a blocker anymore (P0, blocker, means to actually delay the release, which has already happened)."

Although P0 is named as BLOCKER, P1 is defined as a release blocker. The priorities are defined this way for a long time IIRC. Since 5.9 and probably most, if not all, previous releases are released with several P1 issues, either all P1 issues should be lowered to P2 or, more practically, priority definitions should be updated to reflect the way they are used.