Ironic that after the gish styled playtest sorcerer, the sorcerer is now the only caster with no melee options.
It's like they were so scared of the idea that they won't put a melee subclass on the sorcerer even years later.
And ironically the main classes missing from 5e are the Gish and the Warrior on Magic Steroids.
Entirely because of the playtest sorcerer. As that was meant to be the arcane half caster gish, they didn't make a separate gish class.
Then when playtest sorcerer got axed, nothing then filled that void.
Yeah, I think "put their eggs in one basket, then that basket got cut and never replaced" is sort of a theme for the Next playtest. That is, exactly the same thing happened to the Warlord Fighter; despite the crappy edition-warrior rhetoric used in that one podcast, Mearls did explicitly say in a tweet that martial healing was in, and if DMs didn't like that, they could just forbid people from playing it. But then they said, "Hey, this makes more sense as a thing ANY Fighter could opt into, so let's use this cool new Specialties mechanic!" Aaaaand...then Specialties were not particularly popular (I didn't mind, personally, but I get why they were disliked), so they axed them. At which point, they were almost certainly aware that there just wasn't enough time to playtest any new stuff...so they just quietly dropped the subject and never spoke about it again.
The perils of outright
dropping mechanics when people don't respond well to them, rather than at least
trying to make them work: you're constantly going back to the drawing board, despite time being a rather finite resource.
And if there aren't any that perfectly match up . . . D&D can create its own stuff, can't it? It's been doing this for nearly 50 years already.
Oh it
can, sure. The issue is getting people to
accept creating stuff. See also: dragonborn being widely panned and mocked by critics of 4e upon release, yet as of 2020, they were the third most popular race in D&D (after human and half-elf, assuming you split Elf into its various sub-races; if you don't, Elf-combined rises to third, and Dragonborn is fourth overall.)
if all the features are just renamed versions of what the EK and BS have, then yes, simpler is better than new.
Because for all the compelling statements about the need for the class, in the end it runs into issues of "like the Bladesinger but..." and then we have multipage threads about it like we do the Ranger.
See, it's exactly this kind of logic that's incredibly frustrating.
Why would you even
bother making something where "all the features are just renamed versions of what the EK and BS have"? Of course that would be pointless, even foolish. A proper Swordmage should actually have
its own mechanics. Ideally, they should be ones where you can see some kind of relationship to what Bladesingers or Eldritch Knights do, because that enhances the lore of the situation (making EK and BS more like half-steps toward Swordmage, rather than half-steps from Fighter to Wizard or vice-versa), but that's an ideal that may not always be workable.
Hence why I suggested the "Spell Combat" proposal earlier, using runes that ride on top of physical attacks to deliver spells. Or perhaps you literally dual-wield, with a sword in one hand and a spell in the other like how it's done in Elder Scrolls games, and Swordmage blends the two together in its own unique way. Maybe if you hold a spell focus in your offhand, you can shape magical energy into various forms for a round, e.g. a shield of force
or a bonus-action attack
or a temporary utility effect like "pull one enemy into melee range" or "ensnare one foe within 15 feet" or whatever.
It's not
that hard to come up with actually-interesting but reasonably-straightforward mechanics to play around with in this space, ones that differ from EK, BS,
and Paladin. But what can be really, really hard is getting some folks to even consider the possibility that something with new mechanics could actually be interesting to engage with.
Edit:
And, on the subject of D&D Clerics in fiction: I challenge you to find any example in fiction, let's say before 1960, of a holy warrior wearing relatively heavy armor (doesn't have to be plate precisely, but shouldn't be parsed as light armor, e.g. not just leather), who fights abominations in the name of their deity, but
does not fit the mantle of Paladin. I have set the date specifically so that we avoid picking up fiction that has its roots in the Cleric, which is exactly what I'm criticizing.
If I were a betting man, I'd put real money on the idea that the vast majority, if not the entirety, of your examples will come from Crusader-related literature or King Arthur's knights, both of which
very much look more like Paladins than D&D Clerics.