Points in question:

Sadie can singlehandedly murder gem monsters (with nothing but a sharp stick, while malnourished and overtired, in the rain).

Other humans fighting gems? We’ve got Connie with special training and a weapon that was designed for that purpose, and… humans literally bouncing off of them. Sadie’s strength is definitely super notable (especially given Ronaldo’s gem encounter, below, was the episode immediately after Sadie defeating a gem monster).

We’ve never heard anything about Sadie’s dad. (…And, not necessary for the theory, but.. Mail is a government job. Thinking of things like, say, Men in Black, where mailmen are mostly retired from other more secretive government jobs, tell me you couldn’t see Barb as retired OSI or something on those lines. That woman is intense.)

Look at them.

At this point my headcanon Ventureverse includes at least half a dozen other series and things just keep getting more complicated but. :”3