The problem here is that people are not trained on YOUR implementation. Everything you have listed here is very nice to have (offline mode, interoperability, …) , but MS (with O365) or G (with G Suite) are often available for free to students, teachers, and professors at critical stages in life. Just look at Apple with their productivity suite (Pages, Numbers, Keynote). The market penetration is probably worse than L…
You could've said the same about Notion and its current valuation is at least 10B. Don't let this kind of feedback deter you, OP.
As a solopreneur you don’t have piles of cash to burn to make people use it.