Additionally, in airplane mode it heavily doesn't want to translate, in my use case I have to go to saved translations as otherwise it won't even let me type what I need to translate.
I don’t see it as a disadvantage, since Google markets services on both devices you mentioned. Hardly anyone will abandon its iPhone in favor of a Pixel just for a Google service.
So I think it’s ok what Google did marketing wise.
It doesn't seem to do it "live" in the preview without network access, though.
And the translation app seemed to get into a bad state and fail to download the language packs without first clearing the data, saying I need to download the pack, but the language list showing it already was. Though I haven't even opened it since I transferred it from my old phone, so if there's some phone-specific stuff going on that might have got messed up.
The voice recorder transcription is also on device, but I haven't gotten it to work without google play services on GrapheneOS