attack speed is supposed to decrease the time between attacks, not the skill or light/heavy animations themselves, just the delays between.

its mildly useful for some builds, light attack spam. however its not a really fabulous mechanic.

I use flurry mainly on my dw sorc but I clip light attack into rapid strikes. on some bosses I light attack spam while regen-ing stam but maybe a more experienced DW player could chime in.

I know there are people who are both light attack clippers and heavy clippers, so it might come into play a bit which build and style people use.

also, hidden blade is less stam efficient than flurry. flurry has better sustain due to this, and some people prefer the animation.

the channel is a downside, however with use we can see that the range on flurry is ridiculous for a melee ability. somewhere around 6-8 meters. so you can really keep the flurry hitting your target at range, but be sure to get back to say
2m range if youre about to resart light/heavy or reapply blood craze.

hope that helps a little