A lot of dragoons choose to use life surge for Ifrit Extreme so they aren't draining too much the whm's attention.

Whm doesn't need to heal very much in a few events and they only have 4 rotational nuking spells, two of which are 30ish second cooldowns. Not really much damage output to begin with beyond a little bit of burst damage.

Blm already has one of worst combos in the game (in my opinion) and you want to make it even riskier? Having to convert and place yourself in red HP to make Burst do more damage than a thundara (even just convert in general) and then having to rely on someone else to get you out of red hp is stupid.

Bard is already the worst of the damage dealers and they are barely a "support" class. They use their songs once every 3 minutes and their two hour on a burn phase or primal two hour. The rest of time they are damage dealing. If you want to take away more of bards damage dealing, you have to give them a lot more support abilities to do.

Just a few arguments that I'm sure would come up. The reason classes aren't used right now is because they are geared more towards pvp. All the content we have now is party play, once people have to worry about keeping themselves alive against another player, classes will be valuable.