Especially given how expensive it is to run the AI servers, which is where the Rewrite feature occurs, I think this is fine and even appropriate. Because it costs them every time someone uses it, it would be take money away from other areas if they gave this away for free, so better that they charge the people who will actually use it. I like that it's included as part of the Office subscription fee, which is still pretty cheap compared to other large subscription services (e.g., Adobe and Corel charge a lot more for a lot less capability).
Regarding ads in the Start menu, I have not seen anything like this across dozens of Windows PC's since Windows 10 included placeholder Live Tiles for some games and apps. Is that what you're talking about or is there something else? Is this still happening for some people in Windows 11? Who gets these ads? I do use Windows 11 Pro (not Home) and I do have an Office 365 Family subscription. If others still see ads, could one of those be the reason I don't?