Thoughts on a "Tax wealth, not work" economic model?

Recently, an economist and ex-Citi Bank trader named Gary Stevenson has become increasingly popular by advocating for an increase of taxes on "wealth" (specifically those with assets of greater than 10M pounds in the UK) and a reduction / elimination of income taxes on working people (even those with very high income).

His thesis is basically that as the growth of the wealthy (globally and per country) continue to outpace global GDP, without the creation of new productive assets, the delta between the GDP (e.g. 3%) and the wealth of the rich (~5%) MUST come from working and middle classes people (e.g. in the form of increased consumer debt), eventually cannibalizing the wealth of the middle and working classes driving everyone into poverty. Youtube link

A common criticism of Gary's philosophy is that it is very difficult to tax assets, but Gary argues that it is possible as assets (for example US housing, US debt, US sports teams) can not be taken from the country if the wealthy owners do decide to leave the country. Even if the wealthy do leave, their assets will be left for working and middle classes families to purchase which is better for a consumer economy overall. He believes this can be done in such away that asset prices don't actually fall, but wages rise without a significant increase in inflation due to the downward price pressure of wealthy people selling their assets.

Are there any other obvious counter arguments to Gary's thesis and proposals?