I have been in the same situation myself when I was the only paladin when we started raiding Karazhan with my horde guild. After a while I had everything I could ever need from the instance, but instead of dropping out I kept playing until we had more paladins, and then more after that, and then some even more until I threw in the towel completely and quit WoW. So I partly understand his actions with not wanting to get burned out, but he did it way too soon.

When you’re in a guild and you get gear handed to you it’s a investment in your character from the guild. They expect you to keep playing even when you have gotten all the gear from the instance. An officer is definitely entitled to giving him the boot if he don’t plan on sticking around at least until there is a replacement with the appropriate gear.