CMS rich text block useless for responsive designs?

I’m trying my best to re-create client’s newsletter post as a collection page. So far, pretty horrific. All kinds of issues, first of which putting images side by side (something Mailchimp can handle pretty easily, apparently).

But, worst is, there seems to be no control over the size of images per breakpoint? I have an image that’s 60% wide… well, it’s now the size of a postage stamp when I preview it on a phone. Kind of really difficult to explain to my client while the tool he uses by himself to make a newsletter (Mailchimp), handles breakpoints just fine (goes from side by side images on a laptop, to top to bottom images on a phone), but the fancy CMS hosting they’re paying for can’t do it.

Or, am I missing something? Why pay so much for for something that does so little? Getting harder and harder to justify my recommendation (and, thus my being hired, and thus my getting paid). Hope I’m really not getting something.

On top of all the above, how do you even style CMS collection rich text elements, period? There seems to be no documentation on this. The Webflow University video just says “see another video about styling RT blocks” none of which applies at all, as nothing is selectable in the rich text block, other than giving it a class for padding (which oddly, has a state selector lol).