For the sake of discussion it might be worthwhile to have an emphasized role for each hybrid class, such that it isn't ALWAYS subordinate to other classes in that role. Otherwise the balance may tip too far the other way and have only casual guilds bringing hybrids on raids at all. So a better phrase might be 'Jack of all trades, somewhat master of one'.

Its a tricky thing tho, especially since there ARE no pure healing or tanking classes, only pure DPS. Shamans can be DPS or heals, so why are they ranked BELOW priests, who also can fulfill both roles? Then you open up the field to arguments like 'but my pure DPS class has to get close to the enemy, while the mages can pewpew at a distance', and 'why should shamans be able to do as much damage at range as DPS priests, when they get to wear mail', etc.

I wish it were as simple as you say. My main is a mage so I'd personally benefit from less competition. But in the end it doesn't seem like it would affect the enjoyability of the game for most people enough to be worth all the back and forth involved. Sometimes the DPS meters (or whatever) don't really matter all that much, as long as everyone had fun.