Just to clarify, Old English became obsolete in the late 11th century. No modern English is really similar either in lexicon or accent to Old English.

The English of the colonists is a form of early modern English.

A linguist wouldn't support this, because it's nonsense. Several American dialects are non-rhotic, and several British ones are rhotic. There's a lot more to dialect change than a single sound, and there are a lot of dialects to compare.