What if that "closed guild" puts up a pug group for TR'ing, the group has three people from the said guild. Some poor newbie joins and actually tries his best to keep up instead of *****ing and dropping the instant something goes wrong.. Now this group doesn't actually even mind that too much and teaches him a few new tricks. Is that group not contributing something back to the community?
This small guild does however start a shroud group every three days accepting anyone in. They've a very solid base for easy completions and they ask if anyone needs any advice on what to do in the raid. How is that not contributing to the community? Meanwhile a large guild will just do it with their own people.
Every example I've given has actually happened in the game, some by me, some by others, some by players in small guilds and some by players in large guilds.
In the light of my personal experience what you've said here has no basis on what happens on the servers at all.