AU Draenor showing up for recruiting a race into the Horde is much more important than retrieving a few artifacts across every continent, or at least on par with each other. It's biased to say the artifacts are arbitrarily more important just to craft a fiction of 9.3 being cut.
Blizzard is clearly going through problems with production right now, whether it's due to covid or some internal issue we don't know, but even if 9.1 was delayed I don't see why they would skip out on completing an expansion after the disaster that WoD was, unless they learned nothing from abandoning an expansion.
I mean, it could be repeated, but that would indicate they learned nothing. Which, I guess isn't too surprising, but after Legion and BFA, providing a competent and complete expansion, even if the systems are shit, is better than abandoning an expansion and it's players. Because at least they would be trying to fix issues rather than just wait and make a new expansion.
This is the weakest argument here. Every expansion has a middle patch that leads to some B plot, like Nazjatar, Isle of Thunder, etc. They also have (literal) infinite possibilities with the Shadowlands realms. SL feels like the worst expansion to abandon considering they have so many possibilities for patches.