This is a weird one. Both sides can be arseholes.
Trump's kinda right, since Amazon use a huge web of holding companies to avoid tax. While most multinationals do this (and gaming companies are terrible at the artificial IP license fees double-dutch tax dodge), Amazon is a particularly egregious offender (see Project Goldcrest). It goes way beyond just relocating to Luxembourg for a low corporate tax rate.
On the other hand, Trump's just having a go at the Wash.Po. and Bezos. I doubt he'd be saying this about a prominent republican business (I expect Big Oil companies are at least as bad as Amazon).
Also, while I didn't defend Amazon, it's pretty much inevitable that large companies will dominate retail in the age of the internet due to the economies-of-scale.
Lastly, if Trump is serious, then why doesn't he make any effort to change it? He leads the largest economy on Earth, so if anyone can change corporate tax liabilities it's him.