We don't need to have all interfaces consistent between each other (although this integration might help), but we need them to be consistent with themselves.
Offloading the integration work to a standard interface or library is good, but don't expect to extract the best of the interaction with it only - because the best is precisely at the margin, what is hard to standardize, at the moment in time you are looking at it.
Although it is GOOD to have interfaces/contracts, industrialized things of course.
But the majority of the proponents of these I've met in the industry are the same people that do not care about or understand (for reasons - valid or not) the lifecycle or the normative quality of what they're doing, with the assumption of deferring it to something/one else.
And, with the comparison with SOAP... REST is a mess, yes. But it is considerably less hard to understand and wrap around than SOAP. And it introduced so many better practices and outcomes in the thinking and design and exposure and usability of APIs.