So the fairer comparison would be to compare .rmd vs. .ipynb instead of looking at the kernelspecs in .ipynbs to see the distribution of R users. In my experience (I own the Azure Notebooks service at Microsoft), I see very little R usage - in the order of 1% of Python, similar to what other commenters on this thread have seen.
We wouldn't need special viewers in our source control frontend, or git hooks + tools like jupytext, or in-between editor plugins (VSCode)! By not storing state with input and forcing top-to-bottom linear runs, I think the entire field of machine learning would be significantly more reproducible than it is now.
I do believe that we have room for more than one option. The work that we've done in interactive programming in the Python VS Code extension is one possible approach that folks have seemed to like, and that aligns with what you're saying.
We're going to continue to explore that direction in addition to the Jupyter work that we're doing. Stay tuned!
R users are mostly using RStudio.