True, the element.io site offers the browser client first, which I find wrong. On the other hand some of Signal’s choices were justified by “helping adoption” so I guess that falls under the same category.

Currently I can’t find a way to see which client another user is using in the Element mobile app. Not sure if that is even possible. So I guess for really sensitive matters you have to make sure your collaborators know how to stay safe. And of course if your use-case really required a web-client you could just self-host it.

That linked article talks about how crypto in browser is easily subverted. You don’t have to use matrix with a browser client and most people I know use standalone clients.