Thing is it suits both classes a lot.
So there is an argument that there is too much overlap for them to both be classes.
But then that opens up the argument that in that case the class should have been designed to be able to satisfy both the divine and arcane gish characters, rather than being super thematically and mechanically focused on the divine theme.
Though the arcane gish was never about damage and only damage from their magic attacks. There were tons of other possible effects.
Perhaps the Swordmage should flip it around then: using your attacks to cast spells, rather than using your spells to perform attacks.
You could potentially do something like Spell Combat, where with each attack you make, you add an extra "rune word" or "arcane sigil" or whatever. High-level swordmage spells require three or even four runes, while low-level ones only require a single rune. You can empower a certain number of attacks with runes per long rest (possibly with a once-a-day boost from taking a short rest, like the Wizard's Arcane Recovery). Early on, you have few runes and few attacks, so you tend to use only a small handful of spells; perhaps to liven things up, if your offhand is empty or only carrying a spellcasting focus such as a wand, you can take a bonus action to make an attack that deals lower damage (perhaps PB damage?) but counts for stringing runes together, so that you have a better chance of getting out your two- or three-rune spells.
If order matters, and especially if you must declare your runes before you roll, it becomes a very high-complexity and yet still attack-focused class. If order doesn't matter, especially if you declare your runes only for successful attacks (the way Smites work), it becomes a lot more fluid, somewhat more resembling a Sorcerer than a Wizard, and having fewer total spells but much greater flexibility in what they can use at any given time. Alternatively, perhaps multiple spells correspond to the same sequences of runes, so you have a choice as to what you cast--small spell list but most of it is regularly accessible kind of thing.
Pathfinder 2e has a good summoner design. It's more of a focus on a single summon which is improved over time. Almost like a dedicated pet class.
That's the core of my own summoner design as well. I even found an actual name that
truly fits the concept and isn't just a word-salad invention: "Visitant," literally a word for a supernatural being believed to have crossed over from some spiritual plane. My summoner studies the secret, recondite constellations to draw power out of distant and esoteric planes. Visitants are residents of these distant planes that wish to visit the mortal world--whether out of curiosity, hunger, ambition, or desire to help. They tend to have blue-and-orange morality, even the friendly ones, so dealing with them is a complex affair.
I haven't written up the summoner spell list, but my intent would be to have the bulk of the spells that summon creatures or create entities to perform tasks, to emphasize that fluff of working through proxies. The three subclasses--Astral Signs, the "hidden constellations through which you channel the magic of the cosmos"--that I decided on were the Muses (support-heavy, likely gaining access to healing magic not available to other summoners), the Chimaera (merging with your Visitant to make one more-powerful being instead of two separate beings), and the Protean (more about skill, adaptation, and foresight/divination; ultra-flexible Visitant).