Kara bosses =/= 3 min, except maybe Attumen (who has about twice as much hp as Shirrak the Dead Watcher, and is just a gear check to make sure not everyone is in full greens with no enchants/buffs).
Tyr, the problem is, pulls have more than 1 mob. So, you own everyone on dps the first mob, but now you don't have premed cp and shs-ambush dmg, so you fart all over the meters after you blow your 2 dps-yielding cooldowns. Things in Combat and Assass are as good as what you get from the CP and ambush, but they're not cooldowns, and you don't have to open a fight with them.
Seal Fate gives on average 3 bonus CP per mob (this is with 25% crit, each mob takes 35 sec to kill, you get 1 mutilate per 6 sec with a bonus 1 from beginning (50 energy taken from garrote, which yields 1 cp, meaning at full energy at start of fight you get 3.25cp). Each mutilate has 2.25 cp, and you get a bonus 3.25 cp from full energy at beginning of fight. 35/6 gives 5.8333333 mutilates, 5.83333 times 2.25cp gives 13.125 cp per mob, plus an additional 3.25 from full energy makes
16.375 CP for 1st mob as SF (if you didn't want to read my mixed-up messy math)
Now, if you don't have seal fate, but add in 3 cp total at beginning of fight from premed and ambush, you start the fight at 30 energy. First backstab takes 1/2 time to regen, or 3 sec, so after 3 sec plus openers you have 4 cp and 0 energy. 32 sec left, 6 sec per 1cp backstab. 32/6 makes 5.3333.... and 5.333+4 makes
9.3333 CP for 1st mob as ShS
Now of course, when you move on to the 2nd, 3rd, 4th and sometimes 5th mob, you don't get full energy, or premed. Full energy = ~2.3 (rounded from 2.291666666) CP for SF, and 1 CP for ShS (if you add 2 onto the average from premed at the beginning, the damage of premed scales down per mob, but if the total fight time tops 2 min you can choose to waste vanish to gain an extra 2 cp)
So, after 35 sec of 0 energy with both builds, SF yields 13.125 CP and ShS yields 5.833333 CP.
Now, let's say there are 3 mobs in a group, or 70 seconds of 0 energy per mob and one first mob's worth of CP.
That leaves 42.625 CP in an entire fight from SF, and 21 CP in an entire fight from ShS. (This entire calculation assumes that the ShS build does not have Initiative.)
Simply showing the difference between SF and ShS obviously isn't enough to prove DPS difference, but it's a good start. I'm sure some genius like RP can calculate the DPS difference per 1st fight and each thereafter with a standard 41/20 combat mutilate build vs. whatever ShS daggers might take (probably 18/0/43, but that may be what I would just do).
Blech, that was ugly, huh. I guess I'll have to get better at showing my work w/ maths.