cof speed runs
They do cut down a considerably amount of time off your run, yes.
Luring hellstroms, as you mentioned, makes burning them a lot faster since your warriors can deal equal damage to all 3 at once instead of doing the same damage multiple times to multiple separate targets.
Also, the port of the NPC shaves off probably a good 30 seconds from your run, which is substantial when you’re doing multiple runs.
I mean, in the end, having people that cleared out their bags and don’t need to take frequent afks will always, always make a bigger difference (this usually matters more than the profession choice of your group), but when it comes to the run, a good mesmer who knows how to do more than just drop a few time warps and a portal will make a big difference.
Oh, as for an explanation, check out the vid Strife posted: