Some mma fighters who don't train with weapons would do better than some people who do train with them.
I am specifically challenging the assertion that the martial artist (in this case an aikidoka) who trains with a bokken would almost always (someone was even specific to the point of saying 85%, IIRC) defeat an MMAist with a bokken.
I am asserting that, given the relative consistency of the MMA training model from school to school and the acknowledged inconsistency of aikido training from school to school, it is not a given that the aikidoka would prevail. It really depends upon how the aikidoka trains.
I am further asserting that one can be functionally less capable of using a sword if one's training is impractical and creates a gap between what a person can do and what that person THINKS he/she can do.
Finally, I am suggesting that this doesn't have to be a theoretical conversation. It is easy for an individual aikidoka to test his or her specific ability by actually giving a bokken to an experienced MMAist and seeing how it goes.
If you are going with my greater than 85%...
Please allow my stipulated criteria.
If 100 fights happen between various mma vs Aikidoka
And...
If the instructor was orthodox (correct art transmission)
and...
If the instructor was proficient (knew how to correctly teach)
and...
the student was in proper shape (his body and mind could properly perform, the art he was correctly taught)
and...
The student had applied himself in learning the sword art.
(He sought excellence and was good at aikido sword work)
With these conditions set... 85 fights of 100 would be won by Aikidoka... or more.
Now the reason I can estimate is I have seen UFC grade mma fighters go up against weapons. They have no training and have to reinvent the wheel (unarmed vs armed) while a lion is running at them.
Maybe 15 guys of a hundred will get lucky enough to see an opening and exploit it.
But I don't event believe 15 would. Maybe less.
But that would be a wager I would bet.