I am wondering what you are referring to with 'non-chromium' browser market. Typically people don't complain about chromium-based browsers, but about the dominance of Webkit-based browsers (Safari, Chrome, Opera, Edge, etc.) and from that perspective there is more or less just Firefox left.

Nevertheless, that is besides the point as the rendering engine is not the sole source of browser differences. I am not saying the Googles high market share isn't a problem itself, but that Apple is abusing their market position to hold back the development of the web (by not implementing relevant APIs and not allowing competing browser engines on their platform).