You'll never succeed at killing Swordmage-type characters. People want them. They sell well. They can be quite balanced (look at the 4e one--it's arguably one of the weakest Defenders, but it was neat and tricksy, and definitely had its fans.)
Also, LOL, eliminating BOTH archetypes AND multiclassing? No, I'm sorry Lanefan, this is...not something that will ever happen in D&D. Period. There literally hasn't been a numbered edition of D&D that lacked multiclassing. Even OD&D allowed a certain limited flavor of it. The thing you're proposing is--genuinely--in contradiction to what D&D has offered for 50 years.
Frankly, I'm shocked to see you suggest something that is so radically out of step with traditional D&D. Like legit actually traditional here, not "it was done in 3e so it's traditional".