If an offense set provides a 77% increase in damage 100% of the time compared to an crit damage set that provides 100% damage 77% of the time (because it crit 77% of the time), then they are equal. So the % increase in damage than an offense set provides compared to a crit damage set IS the crit chance breakpoint where a crit damage set becomes better than an offense set. If the result is 1.21, then at 121% crit you'd be better (assuming the damage continued to rise which it doesn't, hence anything over 1 means offense is just better) Anything over 1 means a crit damage set isn't capable of producing more damage than an offense set.
This is where you have a missing component. The offense set provides 77% more damage 100% of the time vs. NO SET BONUS. Likewise, the cd set provides 100% more damage 77% of the time vs. NO SET BONUS. You may claim you are not trying to compare offense to cd, but as soon as you start putting them in the same equation (one over the other and determing break points), then you ARE, by definition, COMPARING them. The offense set then no longer provides 77% increase 100% of the time. It provides a 77% increase 23% of the time. The other 77% of the time, it provides a DECREASE in damage (1.77/2=0.885; 0.885 <1).
This is what you are not taking into account. This is actually quite similar in form to a phenomenon known as Simpson's Paradox, for what it's worth.
So this is what I'm trying to show--when comparing the two sets, you are setting up the values wrong because you are leaving out a component of the puzzle. You say you are not comparing the two sets or averages or whatever--fine. But then you need to be clear about what it is you are comparing and what you mean by "critical damage breaking point" and if your question--whatever it may be--is at all interesting to others.
Because when most people say "critical damage breaking point," they mean that point for which the total damage provided by one set is equal to the total damage provided by the other set, holding all else equal. And that is very much so a question of averages, of both crit and non-crit damage.
