I will disagree with you on 2 points:
RE :
numbers. When you say that excluding ANY type of player just causes reduction in number of players is only partially true. Let say we want solo/group no-box server. A guy comes alone and says - I want to group staff with my 12-box team. We say NO - he leaves. Did we just loose 12 players? No lost 1 guy who wanted to do group content solo - therefore he won't be grouping AND he would be competing for content. If we would let him Box - then everyone can box. Then suddenly people who were could box but were fine with grouping all start boxing - and group content becomes EXCLUSIVELY boxer thing.
Its not like I want to intentionally exclude players, but server goal is server goal - you can't have a PvP server when 99% of people don't want to PvP.
Another point is on
"behavior is not a pathogen" . Oh this one is tricky. One MMO dev who worked early in his career on EQ, and then worked on Guild Wars 2 have said that "The game will FORCE players into a pattern and players will observe it". It doesn't matter what crazy rule set you come up with, if there is sufficient desire to play your game/server overall, the players will accept the entire rule set and push others to do so as well. Of course this is more relevant for actual MMOs that have tens of thousands of players, and not Emu server with 20
And finally - yes some players are better than others no matter if they solo, group, raid or box. Some play MUCH longer and therefore can get a lot of progress faster and may even burn out sooner. Those things are natural, but server NEEDS to chose a preferred mindset - if you allow EVERYTHING - then you will mostly get 12-boxers, and then that casual solo guy who likes to group occasionally won't even come because he will feel lost and alone