So, I'm seeing the general conclusion being that any full caster(Or, at least, group of full casters) above, say, level 13 means D&D wins hard. Otherwise, they'd have to play really hard guerrilla warfare and repel the Terrans, but not win, or at least have a hugely brutal campaign. E6, they probably would lose relatively quickly, but with some pockets of very dangerous resistance from the high-level(lv 6) casters.

I mean, charm, infinite minions, minions strong enough to throw tanks with a single blow(Monoliths are fun), large scale death, and the like means D&D just needs to protect their casters. Even non-casters at relatively low levels can do some damage, with things like Darkstalker Rogues and Swift Hunters, Bubs builds, and the like, but cannot win by themselves.

Does this seem right?

On a secondary note: Would it be at all possible, in an OPTIMIZED D&D world, for nothing but mundanes and partial casters to win? What if they were capable of using modern tech they looted? I mean, Water Orc Frenzied Berserkers could probably wreck a front line, and Rogues and Rangers with sniper rifles could do some damage. Wildshape Rangers would also be pretty nasty.