Like 25% of English words are straight from Latin, and up to 75% have etymological roots in Latin (according to one Latin professor). And the grammatical rules are not divided equally by the "source" languages, either. It is an amalgam, but the flexibility stemming from the roots, is not so simple.

(Also maybe hilariously in this context, as a native Finnish speaker, to me English appears as a very stiff language. In my own, word order does not really matter, you can basically create as many new words as you like, with combining words and switching the endings to change their grammatical role, and most words can be bent, to have a lot of different nuance with just tweaking the endings a bit. The classic funny example being: juoksen, juoksentelisinkohan / I run, I wonder if I should run aimlessly around in short bursts.)