In my experience, most characters didn't have an EX-Mode so game breaking that whoever got it first was guaranteed a win by any means, which is how you make it sound. There were plenty of dodge and keep away mechanics to let you play around it. But it was at least a valid mechanic.
As it is, I literally cannot remember the last time I saw EX-Mode in a fight in Duodecim. It is completely useless, because it takes way too long to charge up and activate.