Seems like you're describing event sourcing. I'm building an offline-first app and doing pretty much what you're describing.

> I always end up duplicating almost all of the backend logic into the clients as well

Yep, this is a pain I feel acutely. I'm using dotnet (C#/F#) because it allows me to ship & run DLLs on the browser with Blazor, leading to significantly less duplicate code. F# can transpile to Javascript with Fable (F# + Babel), so that's also an option. I haven't fully vetted Blazor yet, but it seems good. Clojure can also run on the server and on the browser with ClojureScript.

The only other option I see is going fullstack Javascript, and I hate Javascript.