Let me pick up this gauntlet!
They are outdated.
For starters: the penalties received from wearing armor debilitate most players. Only a select few armor types, such as AT 15 and 16 and AT 19 and 20 would be worth your while to wear it, because AT 1 was so darn good that a 35 quickness bonus would yield better protection than all the other ATs. All the penalties for most armors should at least be halved to be on par.
Couple this to the copious amount of defense spells and a character could be neigh unstoppable. Most of my unarmored players' characters reach 75-100 DB easy at level 6. Add some spells that make people misjudge where you are and the occasional +50/+100 DB instant spell and RM is a lot less deadly.
One reason for wearing armor is if you decide to forgo any quickness, and don't mind moving slow, or make maneuver rolls for running and sprinting.
Another reason is that while wearing AT 1, IF your foe managed an OE roll, then you are *bleeped* pretty good.
Another reason for calling the old armor system bad is because it didn't have padded, scale, lamellar and combination armor incorporated.
Wearing a brigandine and maille hauberk was common for professional combatants between 1100 and 1350, but it wasn't in the charts. I resorted to giving it AT 19... which is probably overrated, but the armor was better than AT 18, without question.
This is but one example, but there are plenty more: Oriental lamellar armors, korazin, maille and scale/ lamellae or plate, rod and slat armors, and gambeson/ arming doublet...
So lets hope Unified RM will tackle some or all of these problems!