I know what you mean, and yes it depends of course how much Base Crit Chance you already have and what skill you play. If you are running around with a LongBow it’s definitly more difficult to reach 100% compared to a DreadthornBow in relation to the 4sec ailment uptime per stack. Multishot is usually a faster skill compared to DA, so If you are sitting on low base crit you might be right to go maybe even above 100% crit vulnerability.
Yes, or 150% Crit vulnerability causes enemies to have a guaranteed +5% chance to be critically hit and another 50% chance to cause another +5% chance (=10%) (I hope i am correct with this)
Currently Crit outperforms DoT (Ailment builds). Hail of Arrows is the exception which is a DoT build but not a pure ailment build.