I'll answer out of order. I would allow for UBI to generally be the equalizer, but there are some caveats. I'm looking at it from the middle of the USA, literally and figuratively, so there are issues of poor health, tax breaks, ignorance and hubris about our world that don't apply to Europe or other economic and political places because they take basic needs and protections seriously. Everything in the US is a multidimensional corruption contest buried behind mass ignorance of real costs at decision points. Blind acceptance of aggression and competition has devalued cooperative, sensibly aware, educated people as "losers" if they don't work themselves to death for paychecks that barely cover cost of living, then use credit to keep up with neighbors doing the same(wanting just a little more than they can afford).
The main point is one of anti-corruption and informed purchase in a system of "One dollar = one vote". The typical VAT is based on the "nudge" philosophy of compromise between consumer desires, accessorized 'intentions' and legacy market forces driving toward the illusion of perpetual growth investments without regard to extraction itself. The influence of such a scheme is proportional to the overall priorities of the market, which has all of the decision making vested in present owners, not future people or places. My argument is for the soil and humanity's contribution to its future, regardless of historical 'success' of anthropogenic extraction rates. Where most people see money, I see bulldozers, landfill leaching and wars for territory, water or religious propaganda.
Every dollar that is created by resource extraction is a piece of our grandchildren's air, water or food that is purchased in the market and burned for the sake of proving who can make the biggest bonfire.
The effectiveness of any VAT or sales tax will be proportional to its percentage of civilization's total overhead costs (including environmental damage/remediation), poor health, nutritional foods, education, bureaucracy, security, etc). UBI alone in a country with poor health and competitive dumbassery(consumerism) is a waste of resources. Why pay people to be useless? OTOH, why have an unfettered free market that pays people to destroy their places "efficiently" and gives corporations a tax deduction to brainwash children as hedonistic consumptionists?
My only real problem with the Stagflation argument is the assumption that the things people are doing should actually be done in the first place(competing extractions). We've spent thousands of years separating people from their natural feedback mechanisms, then 100 years using communication technology to convince them that there's an imaginary Invisible Hand watching over the economy, but it's all smoke and mirrors hiding the catastrophic effects until it's too late to intentionally correct our behavior. I am simply proposing that we finish the machine of market society by installing accurate and immediate positive and negative feedback mechanisms that are out in the open, don't foster corruption and paranoia(income tax code that nobody actually reads) and don't depend on boom and bust cycles that are disconnected from causes by decades or generations.