ZG was always 20man
MC was always easier than ZG tactics wise. There is no question about it. All of the fights were tank and spank with decursing. That was it. Major domo was a bit trickier as you had teleports shields and what not and rag was a good fight for the time. ZG on the other hand had lots of bosses with more than just tank and spank it really was.
As for icc25 no, sadly I missed this I quit the game after totc which was just horrible. 10man heroic was easy 25 was easy until you hit anub and he was a brick wall. ulduar by comparison was a great raid on both 10man and 25man. The raiding in wrath 1st tier was easier than catas 1st tier by a mile. which is the best comparison for me to make. (Non heroic as there was only 3drake that was a hardmode in that tier for wrath)
Also its not a different game different rules scenario it really isnt. Most games have difficulty levels for content this should be no different. Your problem is other people getting gear you feel they do not deserve. That really is sad im afraid. I don't care if someone has got a heroic piece of loot that I had to strive to get months later. Do you get angry when people go into MC/BWL when the content isnt current and get gear you used to wipe for all those years ago? It really is a silly argument.