Simple when you apply for a group it shows exactly how many keys you left that week in the baracerts of +1 to +5, +6 to +10, +11 to +15 , +16 to +20 and +2- amnd beyond. So the group leader can decide if they want to invite you to the group base of the keys you left at what level. Since people doing +20 is doing it to time the key so even if you have 100 keys left in +20 it normal vs 100 key left in +15.
But nope, everyone here does not even what others to see how many keys they left. They simply want to "hide" the fact how many keys they left thus any form of punishment even if it is just to show the group leader how many keys you left is consider bad.
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Do you know what a good solution is, then? Don't allow m+ to be posted in the group founder. NO group founder people have to get friends or guilds or just post in trade chat. Simple solution blizzard can wash their hands clean and even post a blue post saying m+ is meant to be done with a co-ordinated group not with pugs so we remove that tools. So now people who complain about bad pugs can't use that excuse anymore.