If an Orc warrior being arch-mage bothers you, then don't do the questline.
Many people simply want to be able to do the various quests without a dozen different specialists, and Bethesda don't need to put "rules" into the game that the player is able to do themselves.
What if your character was a battlemage who was equally skilled in magic and combat? Should the game detect what skills your character is using prior to removing the barricade from the doors of the guild hall? If a character wouldn't naturally do something, it's up to the player to decide whether or not to stay in character or to proceed anyway.
If you don't want your character to be immortal then just toggle off god-mode!! Hey, I just found the perfect argument why god-mode should be toggled on by default!
On a more serious note, what a load of miserable rubbish you posted. Yes, the game should detect whether you have the skills required to manage a mage guild. The game should detect if a player has what it takes to be respected in the long term by a bunch of library-geeks and magic weenies. You're damn right it should. What happens in the mage guild is like a modern university asking a cop to be a dean because he shot some hostage taker. It's complete and utter nonsense that is very hard to take seriously.
Yes, Bethesda does need to put rules into the game because that's what makes a game world feel realistic. If the world isn't realistic then there's no immersion. That isn't to say the world has to be real, but basic logic should not be violated. Just like a bunch of soldiers wouldn't follow some alchemist or librarian into battle or a bunch of eggheads at a university wouldn't like to be under the leadership of a mechanic or an accountant, neither would fighters care much for a leader who can't fight like they can, and neither would mages care for an arch-mage who can't actually do anything magicky.
Obviously an Orc berserker might decide to not do the mage guild quest line, but then again, it doesn't require much magic talent to become an initate and there's no promotion involved during the quest line. It's really just a number of fetch quests and Orc berserkers do those just as well as anyone else, so why wouldn't an Orc do them? It requires meta-gaming of the worst kind to know that one shouldn't do those particular fetch quests because they lead to a rather absurd situation.
Indeed, many people want to do everything with no negative consequences for any choices they make. These people are action gamers rather than role-players, and it is [censored] infuriating to see that what those people want is more important in modern RPGs than doing anything whatsoever to actually support the role-playing.