I mean them having mystical powers seems to be pretty unique.

I'm typing this on my Infinity Keyboard while sitting here in my Infinity Pajamas.

Wouldn't infinite universe accommodate infinite possibilities, which includes the items non-existance? So if they were definitively able to prove the stones exist across all existence, then that could be the differentiator?

Yes, but the Infinity stones called dibs and the multiverse respects dibs.

My infinity poop

The whole Multiverse saga has been bungled.

This scene was great at setting the stakes, the most powerful thing from the last saga are now paperweights. That was a great scene. Loki knew how powerful these stones were, he used one of them,m but now they are nothing. If I recall correctly this was after he tried to use his own magic. So it was confirmation that whatever this realm was, it didn't just work on him, it worked on the most powerful thing he could have imagined.

And then of course you look at the rest of that show. It set up a great villain. The only person who was actually in control of this crazy world Loki found himself in. He acts and behaves exactly as someone who knows everything would. He taunts, he has fun, and he ultimately gives Loki a reasonable choice. Chaos, which could unravel all of time, or order, which means some must sacrifice.

And a choice is made. By... Loki? Other Loki. Different Loki. The same Loki?

That was a hell of a setup.

And then Ant-Man kills Kang.

(And the Kang actor is arrested [and eventually convicted] for assault.)

The Multiverse saga was already having a tough time, but to lose your villain... That's rough from a story perspective.

The other thing, going back to the Infinity Stones themselves is that you needed to nerf them somehow. We do get a Multiverse Infinity Stones story in What If...? with Ultron. So that story is also told.

No one is going to complain when the Infinity Stones don't show up in Doomsday or Secret Wars. But if they do we can point to Loki to point out how they don't always work in whatever magical thing we end up seeing, or point to how they already told the Multiverse stone story.