Kind of comes down to that old argument else where.
No ones online you know, what to do, Quest, train, kill, repeat till maxed.... Top in swards... next magic... repeat. So yeah the old timers are all maxing out Armor, Swords and Magic. They got their characters and names, and starting is pain full, so why 'limit'. if you dont limit they can keep going on and doing something waiting for others and prospective newbies to join (if evil) and go sick em. plus already have that 10+ in mining so mining for something isnt as painful as it would be with a new character. Plus people would have to know X is their alt etc. Easier to go with the same character.
You prevent Warriors from using magic, what are they going to do when maxed out, and they dont want to craft or mine... hava a heart Valentinaaron. (can you read the sarcasm)
But is going to boil down to the DEV and the world setters as arguments go back and forth. AD&D, they had that argument for years. pointed to all the same sources then came up with a solution, a "Battle Mage" with a very limited spell selection, but they allowed armor for it with out the penalties. But they didnt allow the extra perks of a fighter. Thats one solution. Imagine a warrior only limited to healing magic.... and no 'offensive spells, except 'cold' and the like.
Other worlds have magic coming from other sorces that allow magic and armor together as one, as part of an all around concept of a fighter. Others its black and white one with out the other.
If your going to go Magic user=no phyical armor, than they need magic Item/spell to make it capable to the warrior side. After all you get bum rushed by a warrior in full plate, a robe and a wind aint going to do squat. If there is the equivlent, I havent seen it yet.
So I think its up to the Dev/world setters to define thoes lines. Me personaly I always like the seprate issue. Mages cant wear armor. rule. Why, mages spend so much time money and effort, getting the items, spells etc, also have to contend with people who have a lot more time to play than we do, and can power up in both and have the best of both.
My character who originally started out as "Just a bard" now has come to the fact, hes going to need some kind of defense, or some kind of combat ability to defend him self from (evil characters). So now not only do I have to beef up the musical instruments, but now magic, and armor, and armor training, plus ways to make even more tria, and moe PP to pay for it, even then I'm still short in weapons, and don't stand a chance against seasoned characters, and characters that have been on the server for years. So my opinion is biased.
So in short i think its going to boil down to the world setters, and their opinions and a decision their of.
Just my Two Tria for what its worth.