You are right in pointing out that the Web browser isn't the most suitable UI paradigm for highly interactive applications like a scientific typesetting system/text editor.

I have occasionally lost a paragraph just by accidental marking a few lines and pressing [Backspace].

But at the moment, there is no better option than Overleaf, and while I encourage you to write what you propose if you can, Overleaf will be the bar that any such system needs to be compared against.