after extensive testing and theory crafting different scenarios, i so far come to the conclusion that bomb spec is stronger in premades. sins arent very popular in premades and i think its because they have been misused, gameplay style is different between pugs and premades and changing the focus from facestab to soul strike is key.
for firsts, if a sin needs eb in a premade, very likely barb is the better choice
second, 2 equally skilled teams in a premade end up firstly to burn one another's cds before actually killing each other, soul strike gives either a stun with a small 20 sec cd or a powerful bomb that gets poms, shammies and conqs to bubble.
total dmg is bigger, unless sds+gc+ fs has crits on offhand and mainhand or u have every piece or u have crit dmg and crit gear and no critigation happens(but then again u have no cc, and domb+ stun still hits harder most of the time)