I disagree - in fact I'd say that simply calling it "a mongrel" is the gross oversimplification.
Aside from vocabulary borrowed from Latin and French, it's broadly similar to modern Scandinavian languages, and to a lesser extent certain Germanic languages (Dutch, German etc.).
It's one of the main reasons why Scandinavians often sound like far more natural English speakers than anyone else - even if they have never lived abroad or spend much time at all conversing in English.
Because there is very little conflict in grammar and such a huge overlap in core vocabulary - holding basic day-to-day conversations takes very little conscious effort from them, as opposed to Romance language speakers, for example.
A good article:
https://www.apollon.uio.no/english/articles/2012/4-english-scandinavian.html