Viable platforms require viable ecosystems. I don't see how you can get around that fact. That's what sets the lower bound for scale. If you do not have a an ecosystem that's comparable or, alternatively, sufficiently non-overlapping then you can't compete. Amazon's OS crew is relatively small.
Samsung can't compete because there is no viable Samsung ecosystem, and Samsung has not aligned with an ecosystem partner other than Google.
This is false if Android is an open platform. Because then it's "viable" by the very nature that tons of apps exist for it.
The problem is that Google is creating a walled garden, to prevent competing app stores. Apps developed on Android could be easily listed, downloaded, and installed on any flavor of Android. Samsung, Amazon, etc. could all have their app stores, and developers could script a simple command to update their apps everywhere.
However, by creating a proprietary layer like Play Services, Google has effectively made a proprietary fork of Android the dominant one, requiring different levels of effort to support non-Google phones.
Both Google-logo Android and AOSP Android OSs are open to alternative app stores, unlike Apple's products. Where are the garden walls? Conversely, most major apps are distributed through multiple app stores. Indeed that's the only way to sell in China. Only a narrow category of 3rd party apps need Play Services, and almost all of those can treat those APIs as optional.
Samsung can't compete because there is no viable Samsung ecosystem, and Samsung has not aligned with an ecosystem partner other than Google.