> The way I see it, the main problem that UBI is solving is inequality, it's a rich to poor transfer.

The main problem UBI is solving is expensive duplication of function between status quo means tested social safety net programs and the tax system. A secondary problem that it can solve if benefits are tied to revenues and the right dedicated revenue stream is chosen has to do with calibration of benefits in status quo safety net programs.

> At this time, the amount of UBI should be below what allows a comfortable life, because it would lead to a feedback loop in which people would be increasingly demotivated to work.

As long as you don't automatically tie UBI to inflation this is self limiting since excessive demotivation causes critical labor shortages driving both wages and final goods prices up which (1) lowers the quality of life which can be maintained on UBI so it isn't as comfortable as the nominal benefit would seem to provide, and (2) raises the marginal benefit from chosing to work, both of which serve to negate demotivation.