> As far as I understand it, the stance of the 'Open Source' crowd is that if Amazon can't make it one of their AWS offerings then it isn't true open source.

This statement is 100% correct. Open means open for everyone. There's a "but they are providing FOSS as a service on a proprietary platform", which seems like the next step on the LGPL-GPL-AGPL stairway of licenses, but SSPL failed to convince anyone it was a necessary freedom:

- MongoDB Inc obviously had no plans to release their own SaaS platform under SSPL

- AWS source code being released wouldn't have benefited anyone other than maybe other major cloud providers