For now, I use Tidal only on my PC, which doesn't permit offline use, but my guess is that Tidal-streamed files being listened to offline will still be decoded in MQA if equipped accordingly. But just so we're clear: you don't actually "purchase" albums on Tidal, you stream them as much as you want, and pay $20/month for the privilege (although you can put songs and albums, such as Led Zep lV and PG in your favorite albums collection for easy access.)

Is there any way one could download the MQA file from Tidal to use in offline mode??
I'm interested in purchasing Led Zeppelin IV and Physical Graffiti.

Zero experience with Tidal: yes I was surprised that the sound wasn't subpar. And I totally stand by my experience with MQA as marketed to the masses -- unless you're a complete technogeek, I think the vast majority of people out there don't really know what MQA is supposed to bring to the table, and why it matters. Don't be such a grouch, we're all in this together, trying to figure this crap out to the betterment of the society as a whole.

Just what did you expect? Same files = same sound. Many have reported that this is the case.

Then you say "If I could offer a criticism of the entire MQA build-up to this point, it would be that the explanations of the benefits of MQA—presented on a level that would allow easy comprehension by the layman—have been pretty obtuse so far."

This evidently had you quite confused until you "read a very cogent post on the Roon Community site recently which basically summed up the real genius of MQA—it addresses issues of time smear in digital playback."

That is exactly what every article I've read about MQA has said. Less time smear = better sound. What's not to understand?

With your obvious understanding of digital audio, and all the different setups you have used, and all the press both Tidal and MQA have garnered, it is hard to understand how you were surprised/confused by these things.