The problem with having a handful of people be billionaires and trillionaires is that money is power, and with that amount of money you have nearly unlimited power and influence over everyone and everything. A system that will concentrate that much power will be inherently evil, it will and does serve the needs of that few over the needs of the many.
UBI just doesn't solve that, and it especially doesn't solve that when it's being funded by a highly regressive VAT tax that none of these ultra wealthy people will ever pay as Yang is proposing.
Honestly, this whole Yang project just strikes me as a weird 10x play by wealthy bay area VC types to get out of paying more progressive income taxes by attempting to bamboozle voters into a regressive tax based UBI they will shoulder the burdon on, so we will forget about major structural problems like wealth concentration.
Regardless, no, I don't think trillionaires should exist and I'm pretty confused why anybody thinks that is going to work out well for them, competition, or democracy.