Yes, howl debuffs resistance. It's not worth using against a single target, but it makes a large difference against groups of enemies when you're teamed.
Thanks for responding, I wonder why they don't list it in the description when they went through the trouble of listing it in the others? I am glad it debuffs, I would like to debuff multiple targets at once.
Sonic Blast has three cones, which you might have confused. Howl is your basic damaging cone with -res, Shockwave is a 100% knockback attack, and Siren's Song is a Mag 3 Sleep; Shockwave and Siren's Song are the only Sonic Blast powers that do not debuff, giving up their -res in exchange for their status effects. Screech, the single-target stun, still does pack -res (and has a nice long duration on it).
Regarding your "defender first" attitude... stereotype issues aside, everything but those two cones will debuff, and by keeping up a steady attack chain, you can massively amplify your whole team's damage output on hard targets. You're Sonic/Sonic, if I read correctly; Sonic Resonance has powerful tools, but is a very hands-off powerset most of the time. Once you've slapped your buffs on your teammates, and toggled up Dispersion and Disruption, the only active powers from your primary to worry about for the next 3 minutes or so are Sonic Siphon (non-stacking, long-duration single target -res) Liquefy (6 minute recharge debuff), and maybe reapplying Clarity if there are mez-heavy enemies around. If you aren't planning on blasting the crap out of everything, what ARE you going to do inbetween buff cycles? By maximizing your own damage output, you also maximize your team's damage output, and vice-versa.
Rule number six of an empathy defender is NEVER underestimate a blaster's ability to die. I don't care if he has CM, Fort, both RAs, bubbles (both FF and Sonic), and is fighting next to a Storm defender with hurricane on. If there is a way to die in that situation, the blaster will find it.
I read in a few of the threads about adding howl to the attack chain to help with the resistance debuffing, but when I am in the game and read the description, it does not say -res, the first two offensive powers do, but not Howl and another one which I don't recall at the moment. I planned on only getting the offensive powers that will debuff and focus on the sonic primary and pools that help the team. I wanted a character that was a defender first and foremost, and not focus too much on damage. I have blasters and scrappers that fulfill that role when I feel the need to make arrests as brutally as possible.