shrug, if you just drop the ESF penalties for armor, most casters would still face impossability with them. . .you only get X/* costs at 7 or less. . .a magician would be paying 11 per rank for MIA plate. . .and a cost of 7/* isn't exactly peachy.
I do in that respect agree with you, in that there's really no need for both, but the system has two layers of anti-armor logic for essence and channeling, first the casting/ESF penalty, then the really high costs. .
You'd need to do more than just dump the casting/ESF penalties to make armored casters a workable concept, you'd need to re-jigger the MIA costs to make them more palatable, at which point I'd say you're definitely treading into tampering with basic game elements involving balance. . .if you give magicians low armor costs, you make them better, unles you think they're currently underpowered, that will shift balance in their favor. . .
As to "Try it and see". . .Some of us have. . .RM2 RoCo2 and trancend armor. . .the Paladin and Warrior Mage professions come to mind. . .both have taken a considerable beating for being game unbalancing in their RM2 incarnations.
Not to say I haven't played both, and had a lot of fun. . .there's nothing wrong with them, but the whole "round" character concept those fall into, who fight and cast (and perhaps even sneak) well, works better in high powered, high end games. . .I'm not arguing against it, just saying that in result it tends to be overpowering. . .when you make the casters more armslike, you tend to need to beef up the arms PCs to balance the party out, and end up with a party of high end heros. . .and a high end campaign.