Do SMN and BRD need 2 DoTs?

[JowyAtreides]

Ruin 3 and Ruin 2 do different things though, as one has a cast time and higher damage, the other is instant but allows abilities to be weaved. This is more akin to asking that ruin 2 turn into ruin 4 instead of being separate buttons.

You've answered your own question here for Summoner. Miasma has a cast time and Bio is instant and I think different potencies (can't check from work).

Bards rely on DoT ticks critting to proc their songs effects, they arguably care less for the actual damage of the DoT's than for the frequency, so your suggestion would need to come with a damage per half second (for example) counter. They also have a pair of skills that has potency dependent on the number of DoT's are on the enemies so these would need reworking. They've also got almost no skills to play with anymore, I sort of wish they had 3 DoT's personally, such as a fire arrow that does burn damage.