With Theomars as the Leader, he has 69% Critical Rate before runes.
Players need only 31% more to achieve a 100% Critical Rate.
Since the leader skill and passive skill do not activate until battle begins, then if you add exactly 31% more crit rate from runes, your Info page would show a total of 61%. Once the fight starts, that becomes 100%.
The passive skill also gives Theomars the chance to land Crushing Hits (which will never happen if you always crit instead).
Attribute Advantage portion of the skill remains in effect always, even if the Endure portion of the skill goes on cooldown; and even if Theomars attacks during another monster's turn.