Okay, the Orthodox QM is an informal specification of anticipated experimental results, and acknowledges decoherence as a thing. That is good to know.

OK, as pragmatist pointed out, calling it orthodox is misleading. Sorry. From now on I'll be calling it instrumentalist. As for "informal", it's as formal as it gets, pure math.

My base claim is that decoherence can and will become macroscopic given time.

That's an experimental fact, you don't need to claim anything.

Some physicists seem to disagree.

Really? Who?

Why? To my best expertise it is obviously implied by the mathematics behind it.

Feel free to outline the math. The best sort-of-derivation so far, as far as I know, is given by Zurek and is known as einselection.