Well its certainly an update, and confirmation of something I had seriously doubted previously. Is dissapointing, but still not a huge blowout.
It is not said HOW they do not stack though. Are they then treated like 2 seperate sources of double dmg and combined like DS/crit are (take the highest one then some werid formula for the next one). If so its alot less than stacking but still ends up more than 50% double dmg chance over all.
Even if it totally ignores the lowest one, and just takes highest crit % it still ends up being:
42% (48% if soj) crit vs 21% crit +72max off weapon
Assuming a perf robo (95ed/60max

31-147), 130max from charms, and 40max form helm (for simplicity sake, I know this can be higher max or ED) & lvl20 mastery, 1ww base with +2all (ammy + bc) you get ~100% skill dmg. 130str
You end up with robo ww = 102-1046 (574 avg), 695 avg with 21crit from mastery
robo/robo + 72 = 102-1277 (690avg),
835avg with 21%crit [815avg with 3x 20max]
robo/robo + peace = 102-1047 (574avg),
816avg with 42% crit (
850 with 48% crit,
but then gotta add mdr = ??)
Someone else can calculate with honor, I'm passing on that because then you have to change ias frames and summate crit&deadly and how they don't stack but are an increase.
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Summary:
Based on totally neglecting the possiblity that 2 diff sources of crit are treated like DS/crit are (where there is some increase, but not even close to stacking)..... robo/robo + 72max armor has an advantage although its still pretty close. Max/squid armor only equals peace though if your using atleast 3x 20maxers, and only surpasses if you have very good jewels.