Actually... looking at the stats?
Tau Plasma weaponry is about equal to Eldar... sometimes better, sometimes worse. Eldar are capable of bigger plasma guns though (those can go on their ships).
And Pulse Weapons are a hybrid Plasma/Solid Penetrator (ie, magnetically accelerated coilgun, but not particularly fast out of the barrel. The hitting power comes from how it hybridizes the projectile into an energy pulse) type of weapon.
http://images2.wikia.nocookie.net/__...ulse_rifle.jpg
That's fanon, I think though. But hasn't been contradicted.