Earlier quoted context omitted.
"When our grandparents built the hoover dam, the lincoln tunnel and the triborough bridge with a job guarantee that was just money for nothing - UBI with extra steps." ^ this would be an accurate representation of your opinion then?
That job guarantees exceptionally produce useful things doesn't mean that they don't overwhelmingly produce useless things, or things that are more expensive than they're worth.
One could say the same thing about all the little art projects a hypothetical society on UBI might busy itself making. The pertinent difference seems to be one about scale and co-ordination. Job guarantees say we work together–through a centralised power–to build big things. Handing everyone cash leans more towards arts and crafts and consumption.