I don't see these DoTs as a cleanse protection for Plasma Brand, but rather as a "you shall not stealth before me". Overhead Slash and Blade Storm being different attack types (Melee & Force), it allows me to use them as a counter of respectively Force Shroud and Evasion, because I will be able to DoT them again before they try to disapear, and most of the time it screws their vanishing move.
even though OHS and BS are different attack types, it makes no difference in pvp as you will spam them constantly. I very rarely use PB in warzones since its damage is far inferior to both ohs and bs and DoTs are easy to heal. if you aim for stealthers, i have to stop you there - most stealthers wont be put out of stealth due to DoTs as they don't break stealth (as far as i can tell) and scoundrels/agents got their dodge anyway.
plasma brand definately needs some love, as well as whole vigi/veng tree. i really am missing more synergy skills like force rush.