I'd say if you know React or Vue or another framework and it fits your project well, then no. If you are learning though, there is arguably much less to learn (in particular, not having to juggle 3 languages). And if you are building something very serious, it's suitable: nearly all of Grist frontend is GrainJS, and it's a very big performant real-time collaborative long-lived single-page app.
It enables much of what a large framework like React enables, but with a much simpler implementation, less tooling need to use it, and (some may argue) more convenient usage.
[Grist founder here] On separating formulas from data, that's always been an important part of Grist.
In Grist, check out the "Code View" page in the left-side panel -- it shows all the logic (i.e. formulas) of the document along with the Python data model (i.e. all the column names and types).
Also, you can save or download a copy of the document without the data, but keeping all the formulas. So you can get all the logic (and formatting, layouts, etc), and use it for different data.
(No support for solving circular references though.)