I don't think it's a rationalization to point out that it only occurs when the same baseline conditions are met (using the cloud). I think those constraints/specifics matter. I wouldn't be in favor of the policy if they were different (and I'm not even sure I'm in favor of it now).
My personally preferred outcome would be e2ee by default for everything without any of this, but I also understand the concerns of NCMEC and the general tradeoffs/laws around this stuff (and future regulatory risk of CSAM) - and just the general issue of reducing child sexual abuse.