It's the total antithesis of what Destro is supposed to be. We work our butt off to build power and unleash it in a burst. Now we work our butt off to get a DoT?
The great thing about the burst is being able to direct our energy where it will do the most good at the right moment. This dilutes what we can do with the stored energy. When something needs to die "right this moment!" We used to be able to do that. Yeah it's a three second cast, but now it's a three second cast and time for the DoT to run.