In general looks pretty good and I like your list and nice spread of flavor of subclasses.
But I do have a few notes...
1. Spellcasting level.
Primary among them, and I kind of take this as a "must change/integral to power balance" kind of thing...the Spellcasting at 1st level.
Paladins and Rangers, both, receive their Fighting Style and Spellcasting at 2nd level.
Simply put, that's how 5e does "half-casters." The proposed goal of this design is to generate a half-caster (which, agreed, 5e dropped the ball on) with an Arcane/"mage" power base...ostensibly, I presume, to complete the trinity of "Fighter/Cleric half-caster = Paladin; Fighter/Druid half-caster = Ranger."
Ergo, the class structure rather demands that Spellcasting not be introduced until 2nd level.
This is not to say they can not be a "magical" feeling class at 1st level, see Paladin.
You can give them magical flavorful abilities at first level. One suggestion (which handily takes care of another of my notes to come later) would be to give them a kind of innate "Detect Magic" akin to the Paladin's Divine Sense, but with and Arcane angle/slant...and to use your Arcane Weapon feature at 1st level. They're the guys with the swords that are magically charged/do magic (I believe you made it "force," which I would concur is appropriate) damage. That's what they are...what all half-casters (that we've seen/official) in 5e are, Fighters with magic powers...one of which -sooner than later (2nd level)- is spellcasting.
2. Subclass choice level.
By this same token and in the same vein, both Paladins & Rangers don't gain their subclass until 3rd.
Half-casters have 2 1st level [base] features, 2 2nd level features (Fighting Style & Spellcasting, Paladin actually gets a third but you seem to want to follow the ranger track), and at 3rd another feature + Subclass (first subclass features) choice, followed by different options that I see you took the Ranger track with...and that's fine...so subclass features at 3rd, 7th, 11th, and 15th.
Now, at 3rd level, Paladin subclasses get Oath spells that accumulate as you level, a Channel, and a base class feature. Ranger's get choice of 1 option for extra damage and a base class feature. Given that you're following the Ranger for feature progression, and that your draft already incorporates a Bonus Proficiency, I would probably opt to go paladiny here and make 3rd level Subclass features 1) your Bonus Prof (another note that requires some comment in a few) and 2) cool subclass-defining flavor feature. That doesn't seem OP'd at all.
3. Bonus Proficiencies
There does, however, seem to a bit of discrepancy in the general utility/power balance of what the different subclass Bonus Proficiencies are. Case in point: Swordmage - ALL single-handed martial weapons. Ok. If we're taking that as a/the default "Arcane Warrior" [and yeah, needs a better name] guy. Let's look at the rest...
Duskblade gets: medium armors, and shields, and ALL martial weapons...hmm...
Shadowdancer gets: Stealth. Makes sense. Is flavorful...generally useful in a wide variety of situations. I would put this as comparable to "single-handed martial weapons."
Artificer gets: medium armor and shields, AND TWO sets of tools of your choice?!
Eldritch -I mean- "Arcane" Knight: gets ALL armors (does that include shields?) and ALL weapons. Seems like...a lot. Appropriate yes. But a good bit more than the first few...and about en par with the Artificer.
Summoner gets: 2 bonus languages...mmm ok, I guess that's about the same as the single, more widely useful, skill (Stealth) or single-handed weapons, though significantly more situational than either.
I am supposing, from the descriptions (because it doesn't show on my screen from the link) that the base class receives Light armors, No shields, and Simple weapons, right? So, basically, Duskblade then is getting ALL weapons in addition to medium armor and shields. That may fit with what the duskblade is envisioned to be (I've never been particularly clear on it, myself). But then the thing separating "Duskblade" and "Arcane Knight" is... heavy armor, essentially. Shadowdancers get 1 skill, but Summoner gets 2 (albeit significantly more situational) and Artificer (again, the befuddling artificer) gets 2 tools...Artificers and Duskblades (and Arcane Knights) can use Medium armors and Shields...but for swordmages, summoners, and shadowdancers this is a bridge too far?...I am tempted to remove shields from all of them...that's at least a step toward correcting the imbalances.
I think these need some tweaking to arrive at more even/fair proficiency bonuses across the board. Something like redefining armor options OR redefining weapon options OR adding 2 skills/tools...and either define the skills/tools or make them player's choice, but across the board.
4. Subclass Features
Again, shifting everything to beginning at level 3...so something needs to be pulled from all of them. But presuming Bonus Prof and Something flavorful/defining at 3rd level instead of 1st, I'd probably just bump everything back a space and get rid of whatever your highest level feature is. But regardless, something's gotta go so you then should have something at 7th, 11th, and 15th. Right now there is...
Swordmage: Bonus Prof, 1 1st, 1 3rd, 1 7th, 1 11th, 1 15th. Fine. Pick one to lose.
Shadowdancer: Bonus Prof,
2 1st(?), 2 3rds (?!), 1 7th, 1 11th, 1 what appears to be a 15th that didn't get written out (though "Shadow Form" basically tells you what you need to know
). Ok. Need to pick three out of here to lose.
Duskblade: Bonus Prof,
no 1st, 1 3rd, 1 7th, 1 11th, 1 15th. I think I see what you're intending - since the added armor and shields and weapons is so much, you didn't give them another initial subclass ability. If the idea is for these guys to be the most "fightery" then I would say, probably put either the weapons or the armors in the prof and the other in a feature...which it would appear (using "all weapons") might be repeatable for the Arcane Knight (just a thought/at a glance).
Artificer: Bonus Prof., 1 st,
1 2nd (?!), 2 3rds (?!), 1 7thh, 1 11th, 1 15th. This guy needs work. A lot. He's getting far and away more "stuff" than everybody else. This needs some trimming and tightening.
Arcane Knight: Bonus Prof, 1 1st,
2 3rds(?), 1 7th, 1 11th, 1 15th. Looks like this needs to lose 2.
Summoner: Bonus prof, 1 1st (I would probably stipulate that even creatures off the regular familiars list are fiendish creatures and give some visual indication/trait, a cat with red glowing eyes, a fiery orange ferret with devil horns that's always sporting a fang-toothed smile, a raven with 4 legs, etc...) 1 3rd (which is kinda risky, btw. A demon that'll do what you say...for one round/turn...if it doesn't turn on you which it has a chance to do every single round/your turn?!), 1 7th, 1 11th, 1 15th. So lose 1 here, too, and rework the actual summoning part of the summoner.
I think that does it for my notes. But, like I said, overall, a good -and a lot of- effort. Some flavorful tweaks and tightening up to match the existing game and better balance its subclasses among themselves, and I think you're in really good shape.
