Skip the mat and spend the money on a dehumidifier if you're worried. Concrete does wick some moisture but it only rusts metal when the air is already wet and warm. In a dry climate the floor stays dry enough that it doesn't matter. People repeat the concrete thing because it sounded smart on forums in 2003 and nobody tested it. Your four years of dust is better proof than any thread.

Spike cosplayer was right to stare, Bebop wins that fight easy.

Pulling 40 pavers is a weekend of work you'll hate, and fabric under the base wouldn't even fix the joint weeds. Weeds come up through the sand between pavers, not from under the base, so that fabric would just sit there doing nothing while you sweat. The guy at the yard was right about drainage, and you proved it with zero puddling. Hit the joints with pre-emergent in early spring and again in late summer, pull what slips through by hand, and keep your sand swept in tight so there's less gap for seeds to land in.