if im understanding your question correctly, your asking if PCs should be allowed to wear armour and gain the insane defensive bonus granted from the martial arts skills.
this is how i have handled that, if a piece of armour gives a quickness penalty then it entirely negates the defensive bonus provided from martial arts, now i am using what would be considered "the basic rules", standard rules set from the RM rulesbook from 20 years ago, no fancy additional rules that add extra real time to figuring out initiatives and attacks and such.. so...
AT-5 gives no armour quickness penalty would be wearable by a martial arts master
AT-8 gives a 15 point armour quickness penalty so a martial arts user would gain no defensive bonus from their martial arts training until they took off the armour
that being said, i also have a house rule that magickal armour only, reduces the penalties associated with a specific piece armour, so if a PC could find a +15 magickal suit of armour type 8 then it would reduce the armour quickenss penalty from 15 to 0, so if a martial arts expert found that suit they would be able to wear it and have an insane DB, assuming the other PCs let them get it for loot