But that's not the only difference. Not even the only 'main' difference. So you need to figure out if that's the important variable, or if other confounding variables are causing the issue instead. And as you stated, there's a lot of kata in Kyokushin. So the issue might not be that kata is a bad training method, just that it's overused in kyokushin.
And if it is that, you have to determine if it's an all-or-nothing thing. So, for instance, is no kata the best option? Is only kata the best option? Is kata 1 hour per week the best, or 5 hour per week, what results in the most effective fighters?
Which obviously we're not really going to know. You'd have to do an actual study, ideally multiple different and repeated studies, to figure that out. But until then you can't actually claim what you're claiming, you can only state it as a hypothesis/what you believe is the issue. Or get frustrated enough that you can do some sort of study to back up your statements (for instance, go to (ideally multiple) muay thai gyms, convince 9 new people to join each, and in each gym have the instructors teach 3 of them the kyokushin kata, spending the same amount of time as kyokushin people, teach 3 of them the kata but not focus on it, and don't teach the last 3 kata. Then have the fighters from each gym join a round robin tournament and look at the results. Maybe multiple tournaments spaced out 6 months/a year/5 years if you want to get fancy with it).
Otherwise making a claim without having that information is spreading potential BS.