Mythic + Score is both great and bad. If you utilize it correctly, it's a very good way to filter out your group.
IF YOU ONLY LOOK AT THE OVERALL SCORE YOU'RE DOING IT WRONG
You can click on the dungeons and drill down and see previous runs, affixes and group comps.
I'm trying to run a a Teeming Explosive Fortifying 18 EoA. I check and see someone that is que'd has a 1400 M+ Score. Oh look he doesn't have a high Cathedral, who cares? I'm not running Cathedral and that place is over tuned compared to the others. But he has a 18 EoA Clear that wasn't in time, I drill down see he has several 17+ EOA clears. He's done it a several times, once on this affix in a comparable time. Look at his other clears, he has several 15+ cleared in time with this affix. Probably a solid choice.
Oh Another 930+ que, he has all 15+ clears, but they are all sanguine/volcanic/fort. Look at his history, everything else is failed 11-13's in other affixes. I'd go with the first guy even though he had a lower score.
And if you're one of the "Mythic Raiding > M+" Great, you can ignore the dungeon scores and look at their mythic raiding progression and use that.
It's how YOU use it. Not everyone else. Especially since the keystone changes and you CANNOT exhaust your key. YOU can always be in charge of who gets into your group.
TLR = If you're just looking at the overall score, you're doing it wrong and only using like 10% of the system