So your assertion is that Raspberry Pi was using a Zero as a loss leader AND that it was out of stock. And some how this was enough to stifle competing product

So your assertion is that Raspberry Pi was using a Zero as a loss leader AND that it was out of stock. And some how this was enough to stifle competing products? And the competing products you've cited all have "Pi" in the name because they only exist to fill the gaps that Raspberry Pi products don't fill. For example the NanoPi is a Zero competitor that differentiates itself by having Ethernet. Raspberry Pi dominates the market because it was the first to enter it and provides a limited product catalog that has limited churn with comprehensive support and regular software releases. The same cannot be said for it's competition which historically offered horrible software support land quickly iterated on products meaning that support generally only existed for the very latest.