Clusters and roulette rewards aren't specifically made for tanks and healers only. They go to roles that are needed to keep the queues moving. In the end it's the player community that are leaving those needed roles to tanks and healers.

This comment has nothing to say regarding tank mounts. That's something entirely separate from the new roulette bonus.

I say if it helps queues move then let it help queues move. Want the rewards? Queue as the in need role.