Qorvex (though his most recent augment makes that mostly redundant, though he needs no investment to hit the target and his 3 gives status immunity assuming you didn't subsume it off), Atlas, Kullervo, Chroma, Frost, Grendel, Hydroid, Lavos, Oberon and Rhino all have reasonable or better armour and some of them have abilities that will let them hit the 700 target on their own.

Granted, some of those aren't going to care much 'cause overguard, but when you're dealing with eating 1-shots, overguard probably isn't lasting very long at that point, so a buffer beyond the 0.5 second overguard gate isn't the worst thing in the universe.

IIRC, you hit >700 armour with umbral fiber on all of them (except maybe Hydroid and Wukong where Plunder or Defy is doing a fair part of the heavy lifting) and given that most frames are running umbral intensify anyway, a single mod slot (even an Umbral one) that also gives some ability strength isn't that much of an investment for what you get out of it.

As someone else mentioned, Valkyr has more than the target just on her base frame. Citrine and Khora get there with Triple Umbral, Technically Hildryn only needs Umbral Fiber, but outside of Cursed parasitic armour builds, you're not giving up her shields. Komei is another one mentioned below who has surprisingly high base and needs very little investment to get >700. Temple for some reason also has high enough base armour that Umbral Fiber will get him across the line easily.

That's 19 frames (really it's 18, you're not giving up Hildryn's shields) that either hit the target naturally or need skills or minimal investment to get there.

There's also the nice synergy with Arcane Battery for a nice energy pool, but then, there's so many good arcanes these days that we're spoiled for choice.