You are indeed restricted to some subset, which is the only reason multi-cloud abstractions exist to begin with. The problem isn't punching through the abstractions, it's the pointlessness of the abstractions as a whole. Generic public cloud abstractions don't really work because the value is in the specificity. If you don't need that, don't use the public clouds since those are really expensive and impractical versions of resources for generic consumption.

If your project or BU is too small to make use of the specifics of a cloud, just don't use them. And if you are big enough to do so, you're also big enough to not be helped by some application specific IaC flavour of the day.