I have no idea how are you getting these numbers. In alternating attacks you can strike once or twice initially, depending on your attack difference. Here is the napkin math. Difference between D1 and D2 or Toxin is fairly significant, yeah, but numbers are not as bad. 65% vs 18%The Stimmer with two pulverisers has a 3% chance of causing an injury roll before a reaction attack.

The Stimmer with a renderiser has a 55% chance of causing an injury roll before a reaction attack (even with 1 less attack).

The death maiden with two venom claws has a 91% chance of causing at least one injury roll and a 17% chance of causing two.

To be fair we haven't experienced these problems as much simply because we play without new champions. Our group generally does not like new lore, nor overqualified 'super-champions'

1).

Total probability to OOA with a single attack: 0.83 * (0.67+(0.67*0.16)) * 0.66 = 0.43 = 43%, so a chance for a single attack to fail to OOA is 57%.

Two attacks kill stimmer (1-(0.57)^2)= 0.67 = 67% of the time.

2).

Total probability to OOA with a single attack: 0.83 * 0.67 * 0.83 * (0.67+(0.33*0.67)) = 0.41 = 41% , so a chance for a single attack to fail to OOA is 59%.

Two attacks kill Maiden (1-(0.59)^2)= 0.65 = 65% of the time.

3).

0.83 х 0.67 х 0.83 = 0.46 = 46% chance to take 1 wound, since it is damage 1 and maiden has two wounds. To take her out we need to roll 2 attacks and deal damage with both which is (0.46)^2 = 0.21 = 21%

Now for seruous injury roll with pulverize: 0.21 x ((0.67+(0.33*0.67))) = 0.18 = 18%