The browser "won" on seamless distribution. The browser is all the things you said and worse. It conflates the developer API (which could be as complex as the collective human comprehension will allow) with the execution environment (which must be as simple as possible and understandable to mostly anyone). I have a dream that the browser will turn inside out and start losing APIs that will be reimplemented on WebAssembly. But WebAssembly is moving too slowly e.g. with regards to tail calls and parallelism. So it's probably just a dream from now[1].

[1] https://www.youtube.com/watch?v=zlQEQQSqZ9g -> it's an old dream that others have had before.