EzekielRaiden
Follower of the Way
Well, Shardstone's proposal has one neat concept, that the "Pendragon" (as they call it) has been chosen by a mythical weapon destined for eventual greatness in your hands, thus drawing you down the path of weapon-focused magic.Cool! What's their class fiction? What does the base description of the class look like? In short, what is the magic knight outside of mechanics?
Another option is the "rune fencer" or "magic knight" in Final Fantasy style, where they're often the best anti-magic fighters; that seems a fertile field, a class thematically and mechanically specialized in opposing and defeating enemy mages. Given the power of magic and how it can be genuinely devastating, it's honestly a little surprising that we have no class focused on that sort of thing. Even Paladin doesn't really cover that niche; they do have spells, but only the Oath of Vengeance has even a whiff of anti-magic warrior to it.
Third possibility, straight up take the Swordsage and Bo9S thematics, and fuse them with the portal-watcher faction(s?) from Eberron. An order of contemplatives, Jedi-style, that uphold ancient traditions of magical combat that serve to keep the Bad Things out of our reality. Evil "swordsages" might see celestials as nefarious pests denying individuals the right to take what they can with their own strength, while good ones might see themselves as the quiet guardians who ensure that dangerous things from the outer planes or even Far Realm remain far away from innocent mortals.
I assume three proposals (albeit one of them not my own) is adequate to show that we can articulate some useful and distinct fiction? I certainly hope this isn't a prelude to saying (effectively) "well why couldn't that just be a new Paladin oath/Fighter archetype/Ranger subclass/etc." You know how I feel about replacing an entire class idea with a mere subclass, especially if it's a Fighter subclass.