I think that "under 1 MB" represents the size of .NET runtime proper. However, additional required system DLLs increase the download size of a minimal application to the numbers I cited above [1]. Anyway, your example of Amazon's front page is interesting and is a good point (even though, in my quick test out of curiosity, relevant download size resulted in 2.2 MB [not authenticated] and 9.2 MB [authenticated] - quite a bit less, but still ...).

[1] https://blog.ndepend.com/blazor-internals-you-need-to-know