lionx if you havent played the game don't talk about it.
Simple as that, if you haven't experienced it to the level cap at least then don't believe here say. Which is why I won't give my impression on FFXI, personally I think it would be a good game but can't pay for both :P.

I personally have a level 60 mage and a few alts on WoW and
it is designed to be either played solo or in parties. the class balances aren't designed on nerf's or buff's but on group PvE AND group PvP. There are also PvP, PvE, RP and soon RP-PvP servers for what ever you like. The 40 man raids in WoW take months of practice to get the first boss tactics down pat then there is the final boss which in Molten Core doesn't have a 100% stratigy for a successful kill. You can play this game as casually or hardcore as you want and it doesnt penalies which one you are.

About your warrior friend lionx he must just have a bad run with groups or needs to go level and get in good groups/parties. A good mage will not pull aggro from the tank. If a person gets a bad reputation (eg. always ninjas, can't play there class) then it gets harder for them to find groups, thus making it easier to get good quality groups.

Personally I love WoW I'm in a good guild (like a linkshell), and have heaps of fun. It doesn't really get boring (for me anyway) and if I do get bored with my mage I can go make an alt and not have to pay extra money per month. A good reputation with the community and a good guild is a big part of this game.

Thank you for reading
Cernunnos (my game tag, i made this EoFF account when i was younger and liked Yu-Gi-Og lol)