I don't agree with your point on the 'review-app' pattern. While I agree it would be more work to create a 'review cluster' (I assume you mean app + related services + some test data), this is the kind of effort I think quickly makes you do something a
smarter way once you've felt the pain.
Also, companies I've worked at in the past (when sufficiently big) have had "playground" AWS accounts that had a fixed cost for daily all-you-can-use resources. I'd like to think that if you're big enough to think you need >2/3 supporting services to come up with your app, maybe you already have enough traction for that kind of cloud playground account?
I can only speak definitively for myself, but most apps I have built are generally 1 app instance, 1 DB and _maybe_ 1 service for caching. Thinking about how to make these easier to spin up (which includes making sure it's easy for me to make a close-to-production environment as quick as possible), has benefited me, despite initial pain.
Also, if cost is the angle, there are tens of things companies could do, but don't that could bring down cost. Outside of "have more performance-minded developers", "add more computers" is often the cheapest option a company has as far as increasing performance (hence the whole rise of horizontal scalability right?).
I agree that Gitlab should focus on user experience (I'm not sure what you were referring to by "Git hosting"), but I am happy that they've decided to add this CI/CD (and issue boards, and CI), in ONE place.