>Sam held his own against someone with powers/tech that not
>only had he never seen before, but in the universe of this
>film wasn't even known to exist. Even Cross initially thought
>the Ant Man technology was just a myth, and he devoted himself
>to replicating it. Tony Stark probably doesn't even know this
>is possible (there's nothing indicating Howard ever told him
>or anyone else about it.) Given all that, how is anyone
>supposed to prepare/fight this?

Do you think that same thing would have happened to Cap, Ironman, Thor, Vision, etc.? It had nothing to do with being prepared. Falcon is just a lower tier Avenger that they didn't mind doing that too.