Only time you DA syphon strike is if you're about to cap on mp,which is usually during blood weapon. Also, most people are referring to a single target situation.
In an AoE situation you're using DA +AD and Quietus, which are way more effective than wasting mp on DP. It just isn't worth it. Also the blind on DA + DP conflicts with the (meager) mp gain from blood price.

As for your hotbar, that's honestly a personal problem.