Interesting. I found a reference to this in a tweet [1], and it looks to be a podcast. While I'm not extremely knowledgable. I'd put it like this: Tier 1 - fabs, Tier 2 - chip makers, Tier 3 - data centers, Tier 4 - frontier labs, Tier 5 - Model wrappers
However I would think more of elite data centers rather than commodity data centers. That's because I see Tier 4 being deeply involved in their data centers and thinking of buying the chips to feed their data centers. I wouldn't be so inclined to throw in my opinion immediately if I found an article showing this ordering of the tiers, but being a tweet of a podcast it might have just been a rough draft.