A dude going “yeah bro I’m like a thousand times faster bro I get a day’s worth of work done in ten seconds bro” is the opposite of concrete lol.

And then for details he mumbles about “calendars bro and uh, meetings! It’s all connected bro!”

There have been case studies about this. Your buddy, like many thousands of other people, is simply delusional regarding the perceived efficiency gains. People whose productivity literally decreases, measurably, often report that they have more than doubled their productivity.

However, I doubt they'd care to waste time arguing with such a hardened skeptic

Why not send them over? I mean they get their whole year’s worth of work done by the second week of January, right? Even with ten or fifteen jobs they should have tons of free time yes? Or is their financial reality, for some unknown reason, not in line with their enormous head turning productivity?