Not sure if I'm agreeing or disagreeing here, but the point is that the Mac Pro is NOT, and has never been Apple's halo product. Its now a niche product for people who'd be happy with a Mac Studio if they could just connect a couple of specialist PCIe cards (not GPUs) to it. Even the 2019 was of zero interest to anybody who wasn't already committed to Mac.Where are their sales? The iPhones and iPads. Really.
Looking at https://en.wikipedia.org/wiki/Halo_effect#Marketing the first example cited is the iPod.
For the modern Apple, the iPod and subsequently iPhone are the "halo" product. Before that, the original iMac. Before that, we're back to a different Apple that pioneered desktop publishing and was a major force in nonlinear video editing - but even then I'd argue that the "halo product" was the classic Mac, not (say) something high-end like the Mac IIfx.
Now, I think, Apple are betting the farm on Vision Pro being the next halo product.
Another "halo" candidate is Apple Silicon - and the showcase for that is probably the MacBook Air or maybe the Mac Studio where it offers a lot of processing power in a small, low-powered package. Apple Silicon lets Apple build everything from an iPad to a Studio Ultra (plus their goggles) out of just two underlying dies (Mx and Mx Max).
The new Mac Pro is getting a distinctly "meh" reaction because it is nothing to write home about compared to a Threadripper tower with multiple NVIDIA or AMD high-end GPUs because it's not the ideal use of Apple Silicon technology. The alternative would have been for Apple to sink a huge amount of investment into an ARM-based Xeon/Threadripper contender just for the Mac Pro. They've never put that much into a Mac Pro before - Apart from the Trashcan they were just Xeon towers with - in the case of the 2019 - some nice PCIe plumbing refinements.