That's not true. Threadripper has more cores, supports more memory, has 6-channel memory, more PCIe-lanes and so on.
Even the AM4 socket will soon have 16-core CPUs and PCIe4, so it will probably have more bandwidth than any Mac Pro, for a few hundred USD. The world is moving fast, that's for sure.
And yes, AMD's consumer desktop platform is getting a substantial update next month that will put it well ahead of Intel's current consumer desktop platform. But PCIe 4 is also driving up the cost of that platform quite a bit, at least in the near term.
Presumably the next gen Threadripper platform with PCIe 4 will launch not too far off the time the new Mac Pro does.
As has already been pointed out, the base model is pretty much irrelevant and that Threadripper system would probably be maxed out. Also that systems wouldn't run Mac software.
Everything you say is entirely true, but most people buying these new Mac pros simply won't care because it's not relevant to their actual requirements.