Late game mages are literally gods. Be sure to go down the page to see screenshots for the link that I posted.
However your link doesn't address the basic issue that Destruction spells in particular are useless since they barely hit even dent the massive health pools the NPC's walk around with.
Also the hilarious side effect of the various ways which you can boost magic, is that the best mage build doesn't spend any level ups on Magica. Another thing I'd like to make quite clear, is that defending magic by saying that Conjuration and Illusion are still useful, is rather irrelevant. Since we're comparing the basic fighting styles.
Conjuration and Illusion are utility, nothing prevents you from using the Conjuration/Illusion spells right before you charge in with your weapons.
Most RPGs do 'PC: Low HP with stupidly high attack'/'NPC: Stupidly high HP with low attack'. So this is a bit different, but still the same-ish.


Ps. Always take down the archers first.