For me, it's all the commercial, financial and similarly sensitive emails that matter the most. Those companies are certainly not using a free Gmail account for the most part, and whatever paid service they use (GSuite or Outlook365 or other) wouldn't mine this information. With my use of a paid email service that has no ads and promises privacy, this part is handled. Personal emails from those who use Gmail would get mined and profiled, but that's a harder problem to solve. I do try to push people out of free email services and to paid ones that are cheaper and more suitable for privacy.