[_bpo]

Capital expenditures might shed some light on this. I don't think there's enough public data to be clear but in 2015 Amazon (4.8B), Google (9.9B) and Microsoft (5.9B) were at least on the same order of magnitude in terms of CapEx, whereas other major "datacenter" companies like Rackspace (475M) are much smaller.

I don't think you can draw any definitive conclusions from this, but calling it a class of size 1 or 2 is probably an overstatement of Google (+/- Amazon)'s advantage over Microsoft at least.