You are really underestimating the complexity of the task of building a web engine.
Another problem is that Chrome is already ubiquitous and most of the web sites are simply ignoring the Gecko and only optimise against Chromium.
Don’t get me wrong, I truly wish we had more completion and I hope those projects take off and with time become a viable alternative of Chromium but I am somehow doubtful.
Can’t you just use Obsidian and edit the MD files directly in your terminal? I know Obsidian isn’t open source, but as long as the files are MD and I can easily take them with me, I don’t really care.