> I don't see how the inline option is objectively worse for most users. If I had to have ads in my email client I'd definitely prefer inline. My normal email already includes things I don't normally read so I'm already skimming the inbox to select what to read and discarding the rest. Ignoring ads would be no different than ignoring the other things I ignore.
Inline is certainly the worst option for most users. If the ad is always displayed in the same location (a location separated from what you're there to read: your emails) it can be ignored. As big and distracting as they'll try to make it, most people will eventually tune it out entirely, because they already know nothing they care about will be there. The term for this is "Banner Blindness" (https://en.wikipedia.org/wiki/Banner_blindness) and it means that most people will spend very little time paying attention to the ad.
Inline ads are mixed in with the content you care about (your emails). You say yourself that you'd be forced to skim over them along with everything else that you're forced to evaluate to determine if you actually care about that message or not. That means every time one shows up you'll be forced to determine if what you're seeing is an advertisement or an email that you may or may not care about. You won't be able to become blind to the ads because that would cause you to miss important messages you want to read. Ads, legitimate messages you care about, and legitimate messages you don't care about, they will all need to be evaluated and that will require you to read the ad the same way you are forced to read the sender/subject lines of the email in your inbox you don't care about.
Microsoft knows that inline ads are more effective. It's why they are pushing them so hard. Microsoft wouldn't try to manipulate people into selecting an option that wasn't advantageous for Microsoft. They aren't looking out for your best interests. They are looking out for themselves at your expense. Any time they seem to be steering you toward something, that's a warning sign that you should be extra careful.