While I think UBI is a good direction for us to head towards as a society, I have a feeling megacorps would just skyjack the prices of pretty much everything to negate the benefits of UBI (look what happened during the pandemic). We would need some kind of legislated regulatory shift as well that would inhibit price gouging just for because there is more money floating through the economy.
You are probably correct in that racketeering would need to be reigned in, but I don’t really think it’s all that impactful over housing and medical.
We already have what you are using as a worst case, it’s just fully legal and uncontrolled. Rent and medical has been inflating for years for no reason. Because the proletariat can handle it (even though we can’t).