Welfare is better than UBI because welfare ends. Welfare encourages competence and self-reliance. And welfare can be extended in cases where there really aren't any jobs. It can do what UBI does, but without the fatal flaws.
People need an incentive - something they don't have, which they will attain. UBI takes away one of those, your proposal would eliminate the other.
For a depression-era farmer even a little success was still survival and so it mattered. But for someone who doesn't do anything to produce their own goods and so never feels accomplished because of skill or effort, anything less than what the other guy has will be intolerable. They won't work for anything, so they won't accept hard work as a reason why the other guy deserves to get to keep what he produced, and they'll steal it, killing the goose that laid the golden eggs.
But UBI would definitely support that line of thinking. "Dad is given a stipend by the government because there are no jobs for him, so why would I strive?"
But, that aside, why should the productive care whether you do or not? Let's say self-driving cars do put you out of business, but we acknowledge that you didn't really do anything to make yourself employable. Why do you deserve any resources, let alone a comfortable amount, for not doing anything? And deserve, shmerve, why should I be so stupid as to let you take it from me? If I work I'll simply horde a bit of food and then stop working until the UBI stops and you starve, then I'll start producing again. So why not admit this up front and treat you like an excess coyote population? Spay/neuter you, or maybe leave poisoned food(-stamps) around?
Welfare at least is intended to help people become self-actualized and productive, but UBI is designed specifically to remove all incentive to ever help anyone else. UBI is what someone would come up with after reading the CIA manual on sabotage and thinking - how do I apply this to my entire civilization?
And even if something like UBI ever happened, don't imagine that the productive will share power. It'll be a box, VR helmet, drugged soylent, and you'd happy with it.
It can't be anything else, and everyone should realize it. There's no UBI-topia out there for people, should they simply come to consensus and demand it from their pols. It's wishful thinking and the simple concept hurts more than it helps.
Be afraid of the person who offers you this nonsense.