Pro-level par is the only real par, just like Open is the only real competition.
However, people prefer having a shot at winning erstaz competition over being humiliated in real competition. So, we have something like eleventy-eleven divisions available.
When playing a course outside of an event, the competition is the par for the course. People prefer having a chance to be under (or within sight of) a softer par instead of being humiliated by real par.
And, just like all those other divisions need to describe who is not allowed to enter them so they are consistent from event to event, the skill-level pars should be labeled as something other than just "par" and be consistent from course to course.
In the future when the open division can sustain itself and separate itself from the rest of the game, maybe you can make a case that Open is the only real competition. It is safe to say that Open is the top level competition, but players in other divisions are also competing up to their level of skill.
It seems harsh to say other people don't want to be humiliated if they aren't playing open. Since manufacturers, as well as pro divisions rely on am divisions to subsidize their prize pools, I think it is a reasonable expectation for am players to be able to compete against others of their skill level. Either they progress through the ranks to pro / open divisions, or they stay in the game and stay in their division. I don't see it as a matter of not wanting to be humiliated, I see it as people wanting to enjoy themselves in exchange for their support of the game.