Sure, maybe not entirely isolated. I just mean that the geographic isolation of being an island means you don't see a dialect continuum between English and other languages the way that you do with say, the various Germanic languages.
> isolated
I would say the opposite. Frisian etc. were much more isolated and therefore developed more conservatively.
> a dialect continuum
You do a bit, e.g. Scots which developed somewhat independently/in parallel to English.