What we need is a subset of HTML features that are known to work across all major browser. From Firefox, Safari /WebKit on other MacOS, and Chrome.

Or something that compiles to the compatible HTML code for those platform with 100% accuracy.

Unless that happens, you are dealing with godzillion number of edge cases in hundreds of different System Browser.

But even if such language or subset of feature exist, it will still not be as good or as be limited compared what is possible on top of current Electron. Which means from a user perspective, the Dev is optimising for something they rarely cares about; download size. Given memory CPU and Memory usage to electron.