> that would eliminate the 60% or so of the federal budget dedicated to the aggregate of all social welfare programs

The combination of UBI and healthcare largely should. UBI serves as a better alternative to most such programs (and has much less administrative overhead).

Also, any form of UBI will likely result in substantial spending increases (trickle-up economics is well-established as actually working, incremental dollars handed to the average person are typically spent, not saved), as well as reducing structural friction in the labor market (people can change jobs more easily).

> Without more productive capacity

UBI will also likely result in more businesses/entrepreneurship, R&D, and other substantial improvements to productive capacity. Studies generally show that UBI does not cause people to substantially leave the job market.