Finished the main quest, finished mage's guild, finished SI, more ruins/forts/caves explored than I would care to count, finished a number of user mods such as Lost Spires and VH Bloodlines (both mods nearly as long or longer than the main quests). Leveled well into the early 30's, 250+ hours. Does that count as getting very far?
And you played on decent difficulty, without any balancing mods, with magic skills as your majors? Without training? Without ever using daedric armor, which is the most enchanteable, just with robes, which aren't very and are only one-piece? Difficult to imagine, but I bow before you persistence. Still, even you would probably have to admit that it required a lot of tedious micro-management, due to the game not being balanced for such a character.
School of Destruction becoming useless at higher levels once everybody and their dog started to have Reflection was just one egregious example of the devs really not thinking it through, IMHO. And IIRC the Illusion spells were so expensive magicka-wise that it was a good while before they could be truly useful either for concealment or for self-defense. Ditto shield spells. Etc, etc.
At least this way, the devs will have to really think about balancing of spells, enchantment values of mage gear, having multiple pieces of it including a headpiece, etc, instead of just assuming that if going got tough, a mage player could always grab a dai-katana and a suit of armor. And BTW, using the "bound X" spells for armor/weapons would count for this too, because fighting with a weapon is fighting with a weapon, whether it is summoned or not.
Now returning to the topic - holding a two-hander in one hand is possible sure, but either fighting or blocking with it this way isn't. So, the only sensibly way to implement it is to make the player unable to fight while they cast a spell. Which would be functionally the same as switching between different load-outs.
Also, let's not forget that fighting and magic use 2 different pools of resources, so combining fighting with casting can (and in the past did) very easily lead to very overpowered combinations.