While I understand this sentiment, some people simply suck at writing nice emails or have a major communication issue. It’s also not bad to run your important emails through multiple edits via AI.
Seems like there are potential privacy issues involved in sharing important emails with these companies, especially if you are sharing what the other person sent as well.
Almost all email these days touches Google's or Microsoft's cloud systems via at least one leg, so arguably, that ship has already sailed, given that they're also the ones hosting the large inference clouds.