The whole idea of merges/PRs etc is to be able to formalize this stuff, track it, keep history etc in a way that is open and can be used with multiple tools.
Using some kind of proprietary, or even open source, web backend SaaS completely defeats this.
And the whole 'real time google docs for code' is going to be incredibly intrusive for most experienced devs. People dont make a habit of micro inspecting every line of code someone writes, no one has the time for that. The whole idea is to have good design practices, unit tests, CI/CD etc, good APIs and interfaces.
Sturdy sounds great for small startups who are all basically working on a single shared file and everyone is doing some sort of massive pair programming. That simply doesnt work for other models and is a nightmare. Learning git (or any other vcs) is a tiny tiny part of software development, its not a barrier like its being presented unless you are a junior dev starting out.