I'm not debating which is "best" (well maybe I am since I do use one over the other), all I am saying that having swelling winds is viable. I don't really have any problems with holding aggro with either spec to be honest. Is using OHS probably better for single target boss tanking? I would most likely agree. But the swelling winds spec buffs the weakest aspect of guardian tanking (ae tanking) to the point where I can hold packs fairly solidly against flyby's/mortar volleys/forcequakes/even smash specs. Yes, I know it's just trash and most people don't care about trash (I do!), but it also does help vs the trenchcutters on NM Kephess. I just feel like the single target threat difference between the two is pretty marginal. It's just a personal playstyle preference.
It has been a while since I used the OHS spec. I could have sworn it was yellow and didn't miss, slash most definitely does. In-game tool tips for the two abilities on my guard (gear is full hazmat/ full dg minus helm mod/enh) are: slash 1187-1359 for 3 focus and no CD, OHS 1748-2004 for 4 focus and 9 sec CD. Throw in buffed/more frequent sweeps and I think it's fairly close. I do pretty much do only use slash when everything else is on CD or need to dump focus. It's not that inefficient though (see below).
Been kinda lazy with logging of late, but here are my average threat/ability numbers for a NM FB/SC kill from a few weeks ago. I tank SC/kite phase 2 so my riposte numbers are gonna be lower than normal for most encounters (excuse the formatting).
% # Action Avg Threat
1.27% 12 Dispatch 3315.17
1.34% 16 Force Sweep 2628.94
1.8% 23 Blade Storm 2450.57
2.13% 29 Master Strike 2295.86
0.93% 15 Slash 1932.07
0.26% 5 Force Push 1620.6
0.38% 8 Riposte 1475.25
1.27% 30 Sundering Strike 1323.1
0.21% 7 Force Leap 948.86
0.22% 9 Saber Throw 770.78
0.64% 57 Strike 350.63
0.43% 138 Burning 98.13
I'll log my next NM EC run as 17/24/0 and post a comparison. Will be interesting to see the actual differences between the two.