AWS Lambda has a major head start and is a big reason for its head of vision above Google. Don't get me wrong, Google has a great quality cloud, but the pace and breadth of Amazon's offering is breathtaking.
One of the big controversies was IBM Softlayer being reduced to niche status, which led to howling of a volume never heard out of New York... which delayed the report months... but Gartner stuck to their guns. It's a pretty fair report.
I think you can replace "Cloud" with whatever technology Gartner or most analysts write about.
These firms are little more than uninformed hype producers that fuel the enterprise software spend cycle through marketing (webinars, "research", tap-my-back-events and 3k€ "reports") that tell CIOs/CTOs what they should already know, by definition of their function: what technologies to consider for their business problems, why and how.
On the other hand, they provide a nice scapegoat when someone needs to offload responsibility, a bit like the "no one ever got fired for buying recommended by Gartner".
PS: wish I could find Zed Shaw's video on "calling bullshit" (or related), as it includes a nice anecdote on dealing with industry analysts.