Actually Pulse Phasers aren't indiginous to the 24th century, just because we did not see them until Defiant. Wether fired in Pulses or streams or beams is irrelevent, it has to do with the style of the FX being used in each Trek show, and then the excuses are made up to follow suit, The particle canons used by Enterprise Nx 1701 became twin beams when phase canons, and Pulse like phasers for Trek 2 the wrath of Khan. One could easily define the Khan era Connies Phasers as "Pulse phasers" if you look at the Fx used but that is semantics.