Given their extensive expertise in browser and OS plugins, I understand this move.
You can foresee a challenging future for the Grammarly product for a long time. Now that the "improve writing with AI" feature is everywhere, there are fewer reasons to pay for their subscription (e.g., I didn't renew this year because I have multiple AI subscriptions, and Grammarly was the least critical of them).
However, for me, the main advantage of Grammarly was the user experience of having mistakes and suggestions inline and just a click away while editing, as well as the quality of the suggestions (with an LLM chat, there's a lot of trial and error and junk you need to filter out).
I understand their move, but I wish they had developed a good minimalist native text editor with the same Grammarly suggestions and click-to-correct interface.
That is my number one issue with startups. They all start minimalist and end up bloated, some sooner than others, and what made them great disappears behind all this bloat. See: tyranny of the marginal user.