The fact that you're making the burst take such a long time defeats the entire point of it being a burst. It's not that people couldn't react to a SMN burst (because realistically, it's actually one of the few that can be counterplayed with a well timed purify), but that it's relatively stronger with it's ease of use and lower effective cooldown.
Purify on it's own is an incredible cooldown. Unless your opening burst was contingent on getting it in sync with your team, a bind on a dps at worst prevents them from dpsing and would honestly be better off used for keeping your healer alive or removing something like full swing. Compared to sleep where the healer themselves can't do anything about it unless they/you use purify on them.