Quick and dirty number crunching--
A Bard with a base critrate of 15% is constantly at 25%. Every dot on the mob has 25% critrate at least. This is bare minimum (on average) 1 in 4 dot ticks causing a BL/RoD proc. That's an average of 1 per 6 seconds in a single-target fight, and it's a maximum no matter what of 1 per 3 seconds no matter how high your critrate goes, due to the way dot ticks work, unless you godmode and hit the proc immediately as you get it and the other dot ticks immediately for critical giving you a new Bloodletter. Not sure if that's something that should even be taken into consideration.
Bards have the following oGCD skills to weave into their normal rotation:
Bloodletter - 150 pot / ??s
Repelling Shot - 80 pot / 30s
Blunt Arrow - 50 pot / 30s
Empyreal Arrow - 220 pot / 15s
Sidewinder - 250 pot / 60s
The first 3 are available from 52-53, which is where we're wondering if you can reliably get gains from WM. The way to look at it is to figure out the standard action PPS of a Bard and compare it against their AA PPS and see if boosting the action PPS by 30% with no other changes would eclipse AA PPS.
Correct if I'm wrong, but - barring any SS procs (since those would be identical in either situation and wouldn't change things by any notable degree), a usual Bard "rotation" would look something like (assuming 2.4s gcd):
SS > WB > VB > HS > HS > HS > HS > repeat.
Might be a bit longer, optimally, so we'll use this as a marginally sub-optimal version to see if it'll still outweigh the gains from autos. We're gonna assume 100% uptime on SS and our 25% crit rate from earlier (so 75% of the time we do 100%, 25% of the time we do 155%). The time of this rotation would be 7*2.4 = 16.1s. Numbers time.
Base hits:
140+60+100+150+150+150+150 = 900 potency.
Adjusted for crit, that comes to 1023.75 potency.
~63.58 pps.
DoTs:
45+35 = 80 potency.
Adjusted for crit: 91
That's 91 potency every 3 seconds.
~30.33 pps.
oGCD skills:
Rep+Blunt
130 pot / 30s
Adjusted: 147.875 pot
~4.93 pps.
Bloodletter~
By earlier calculations, I'm assuming an average of 1 reset per 6s.
150 pot / 6s
Adjusted: 170.625
~28.44 pps.
Altogether, we're looking at a total for skills coming to:
~127.29 pps.
Auto-attacks are a little trickier to calculate. All the endgame bows (190+) are a delay of 3.04, and autos are 100 potency (approximately, if you compare their damage to a skill's damage).
So ~100/3.04 = 32.89 pps.
Comparing these two, we see that
32.89/127.29 = ~25.84%
It's damn close, and I might have mucked up some calculations here and there, but this looks to me like WM is a strict dps gain even before you have EA and IJ, at least when you can stand stock-still and perform perfectly. And without WM up, you need to be hitting all of your autos (strafing/lockon) or you're losing EVEN MORE by not having it up.