The "alien uber" hypothesis. Hear me out on this...
For UAP stories where exotic craft seem to operate alongside totally conventional helicopters, trucks, and armed personnel, the cleanest explanation is not that humans secretly built antigravity craft, or that aliens need human help moving bodies or cargo.
Both of these are too hard to swallow. True mastery should have left enormous technological spillover, while a physically present NHI with exotic craft should not need helicopters, trucks, Marines, or security contractors to do its errands.
A more coherent possibility is that a small human faction has learned to access pre-existing non-human infrastructure: a black-box planetary transport system they can summon and use, but not understand, reproduce, or fully control. That would explain the crafts exotic performance, the ordinary vehicles and mercenaries, the extreme secrecy, and the total absence of visible technological spillover.
In short: Not secret human antigravity, and not aliens outsourcing logistics to us, but humans squatting on legacy alien logistics.