I don't know about any security brochure, but I know I can setup 2FA to use push notifications (not an insecure SMS number), and can check where all of my logins are from, and have "suspicious" logins blocked automatically, etc, etc. I can also create single-use passwords for insecure devices (such as a youtube password just for my apple TV). Not to mention how amazing they are about spam detection.
I think their security posture is actually excellent.
Yes. Most definitely. I don't use Gmail and I recently had a discussion with my coworkers about Gmail. When I asked why they use it one person said, "because it's Google" and another said, "What else would I use? Yahoo or Hotmail? Hahahah". A third person responded by saying , "it's just easy because it's Google so it connects to everything else from them."
That said, even though the argument is a bit flawed here, I think most attracted by it would still prefer ProtonMail for other sound arguments.