We do not know which of 1-7 are needed by which people, so giving them to everyone is wasteful.
In addition, providing those basic necessities for free destroys the paid market for those goods and harms economic growth.
> UBI is, in essence, an attempt to create a mixed economic system that is communist at the bottom end and capitalist at the top end.
I think you do not know what "communism" means. There is nothing in UBI about public ownership of the means of production.
> If the subsistence-level of existence is guaranteed, there is no longer any leverage provided to a person with more resources by virtue of the poorer person needing to accept a bad deal in order to live, while the richer person can walk away from the table without meaningful consequence. Workers cannot be as easily exploited if everyone can afford to quit their jobs.
This is exactly why UBI is a good thing. Workers are freed to find the most effective use of their skills (rather than relying on capitalists to do it for them) which will hopefully lead to higher economic efficiency.