I keep my Kindle on airplane mode all the time so this wouldn't work.
https://www.nytimes.com/2009/07/18/technology/companies/18am...
Are kindles that better than standalone competitors?
I have an iPad but don’t like reading on it (too big and heavy) , and was previously reading on an iPhone XS Max, but even the phone feels heavy to hold while laying down after a while.
No, but the nearest competitor, the Kobo Clara HD, is rather recent, is only a tad smaller for the same screen, and also requires a "login" to activate.
However the Kobo takes .epub files without further ado. I think Amazon lost the format war, not that conversion is hard (cf. Calibre-ebook)