There's this notion I don't see discussed often. The more distant/unstable the link is between a caller and a callee, the more coupled they should be. The closer and more reliable the link is, the less coupled they should be.
That's why when we build interfaces in a single codebase, we can let them be minimal, and let callers use loops for batch operations. But when talking over network, we build elaborate protocols and languages (e.g. SQL) to allow for more complex operations in one roundtrip.
So if one is trying to treat their backend like it's part of their front-end's codebase, that can be fetched and looped over with little regard for the many failure modes, they're going to have a bad time. The front-end to back-end is one of the most distant and unstable links we have in computing, if not _the_ most unstable. This also applies to any intermediary back-end over network.
Minimize network interactions, and shift most work into the single backend codebase for maximum reuse and reliability.
And if you just talk about having 1 api for 3 front-ends, aren't you then forcing your front-ends to contain a ton of business logic to figure out how and what to display based on your API? You could've just given them what they need, but instead they're forced to weave together some insane tapestry from all kinds of "generic" endpoints you gave them? Isn't it expensive to maintain those front-ends?
The GP frames the problem as merely avoiding round trips. You introduced the idea of eliminating redundant database calls on the back end. In that scenario, you absolutely have the right idea.