GearScore was never mandatory. In WoW, while a group is assembling a player is in direct competition with other players for spots. If a pool of players available allows for a steeper gear/knowledge requirement then what is actually required for the run then why not take advantage? Players forming groups often check armory or others in game that do not have GearScore and allowed them into groups.
So what if you don't get a spot, that didn't ever make GearScore mandatory for participation. All it did was make the player aware that a more advanced player pool exists. One that will ignore players until they put in the time to get caught up.
Don't bother bringing up that GearScore is a poor indicator of Knowledge/skill/or gear choice. it is a well know fact and is just a tool for estimates before proper inspection or viewable performance. If you know in your heart that you can compete, it is on you to show the community by putting forth the effort.
Deadly boss mod takes information that is already available in game and smash's it in front of players. Not mandatory just easier for some players. Some will argue that it makes the game to easy but i disagree. Text in a combat log is no different then text anywhere else which is no different then someone giving directions on vent. Same information just a different delivery system.
If you are behind the curve, play with others in the same situation.
If you can figure out how to do a fight/coordinate with teammates through default delivery systems then do it. If people in your group need you to have to mods so that they can do their job, find new people or help them out by getting it.
I don't feel like what i have said is elitist or rude. I think often community members take out frustrations on things like GearScore, combat logs, or W/E because it is easier then examining the true cause of their frustration.