Statistically, a 33% crit chance means that each toss of 3 grenades will have at least one crit 70% of the time. That means that 30% of your throws will have 0 crits. In fact, you'll have nearly a 10% chance to have 0 crits on 2 consecutive throws.
If you get up to 50% crit chance, you'll have a 12.5% chance of not critting. If you get up to 60%, you'll drop down to 6.4% chance of not critting.
The more might you stack, the better the rabid/rampager options look compared to carrion.