[contingencies]

I think your assumption is that cloud providers with different features cannot be abstracted without making the whole abstraction 'leaky'.

While your perspective may hold for a traditional, rigid, single-layer, abstraction layer with the most simplistic, binary-level feature presence, it does not hold for better formed solutions. From https://en.wikipedia.org/wiki/Abstraction_layer: All problems in computer science can be solved by another level of indirection (David Wheeler).

Some real world differences between cloud providers: available hardware, available installation images (OS images), available bandwidth, available logical location on the internet, available physical location (legal jurisdiction, etc.), scale-out time, cost model.

How do you conceive of these differences, and then deploy arbitrary services to an arbitrary number of individual instances running unique combinations of cloud provider specific features on unique cloud-provider deployed OS images in parallel? There are various approaches, but it's not that hard to come up with a functional set of abstractions. Think about it.