Of this list, I would say that Antimage Warrior, Magic Police, Portal Guards, and Elite Magic Defense Force are actual themes. The other ones are merely how a magical fighter mage is doing what they are doing.
The most basic difference in 5E between a Paladin and a Fighter/Cleric is the theme of this person believing so strongly in a cause that they swear an Oath that actually gives them magical ability. The difference between a Ranger and a Fighter/Druid is that the Ranger is specifically a tracker and one who is meant to lead others through the wilderness safely. So for a similar gish... we need something that this class does or belongs to that isn't the same as what a Fighter/Wizard is. Those ones I pointed out would definitely work in that regard, because they are all specifically something that this magical warrior does that a baseline Wizard does not, just like the Ranger specifically does tracking and survival for themselves and others that a baseline Druid does not.
The question then being whether a magical warrior that is a planar guard or a noble defensive knight or a cop that goes out to take down unlawful magic-users is a theme that other gish people would want. It doesn't sound like it though... it always seems like they want completely fluffless warrior mages that are like Fighter/Wizards except they get their own special mechanics. And that's why the identity has never gone any farther, because the Fighter and the Rogue are the only two classes in the game that are just umbrella terms for a bunch of thematic identities that come out of the subclasses. Every other class has a theme built in.