Decreasing people's personal income taxes doesn't seem that bad. Has some effect, but not that world changing.
You still have a variety of other taxes used to help with funding the government with things like capital gains taxes, sales taxes, and so on. Suppose an issue is you don't really want to scare off the billionaires from keeping their money/businesses in the US, since then it can be taxed.
Reminded a bit of the some of the scandals that have occurred over the years in Europe where people were found to have been making sure they were receiving their pay to an entity they formed within the US, so as to enjoy the lower taxes. Think Jimmy Carr had that happen to himself. Since it really is an incredibly inviting tax environment that attracts people wanting to dodge taxes in their home countries, helping subsidize Americans' government spending.
So while you personally may want to imagine populism involves needing to be at war with the elites on every level, it's worth considering that they're in an obnoxiously powerful position that necessitates having to still live with them.
Though I think many consider populism to more be about helping the population in general, which doesn't really require that you be against those sorts of tax policies. Like wanting a higher minimum wage doesn't mean you are required to want higher capital gains taxes, even if it might be satisfying to do so on the surface.
Trump has honestly done some stuff though in the Tax Cuts and Jobs Act, to force a tax on accumulated earnings of foreign corporations that occurred within the US territorial system. So companies like Apple, Google, and Microsoft would be forced to pay billions in taxes to the US.
For example:
Apple, which has 94 percent of its total cash of $269 billion outside the United States, said it would make a one-time tax payment of $38 billion on the repatriated cash.
That particular tax was a bit funny as it resulted in some stupid sob stories ending up in the news about businesses, legally located in India, being forced to start paying taxes in the US for money they'd earned here. They were making a point of not accepting the payments within the US since they wanted to skip paying taxes were at all, in spite of actually working within the US. So populist policy has helped to avoid these completely absurd tax dodges. Believe SCOTUS ruled against them last year by the way.
So I suppose I would question whether populism really requires a specific tax policy if the end goal is to achieve a better outcome for the population.