The Fighter's a fine class, but in terms of play with subclasses, the core build has far too much power.
Hmmm, I think I am in the camp that disagrees with this. As I try and move more things to the fighter archetypes, I keep wanting to put them into every fighter archetype, effectively putting them into the core class. So as I try and objectively look at your breakdown, and it's obvious you put plenty of thought in, I keep thinking that you're deviating too far from the other core classes for my taste. Especially the part of getting your Archetype at 2nd level, does not sit well with me. So, I don't think I have anything constructive so say about that.
However, your reply to that concerns a 1/2 caster fighter. And I agree, that the Eldritch Knight fills the Fighter/Mage role pretty well, with the emphasis on Fighter. A Bard fills this role, but the musical flavor element is too strong to diversify much. Bard is not the answer. So while I think the Fighter class can be left alone, I think it would be nice to have a 1/2 caster class who's archetypes gain parts of the other classes.
So. I might suggest a new class that is a 1/2 caster but whose archetypes take on attributes of other classes. So you can have effectively a Mage/Fighter with emphasis on Mage, a Mage/Thief (does anyone actually play arcane trickster?) maybe a Mage/Cleric with some limited Cleric casting, etc. I would think this adventuring mage would borrow heavily from the structure of the bard, but keeping the musical shtick out of the picture. I think your Spell Knight would make a perfect candidate for this, as would a Spell Sneak, or a Spell Hunter (Mage/Ranger?)
If that's not the direction you want to go with this thread, say something, maybe we can have a different thread on this aspect.