It's more about how people define the term. I don't think I've seen the position made disingenuously.

Most people I've spoken to think of creole as a mixed language that becomes it's own language. To them that describes English and how it came to be.

Even if you require colonisation to be part of it the position can stand. The Anglo-Saxon's colonisation by the Romans and the Normans are a big part of how the English mixture was formed.

If your definition requires an indigenous, non-European, language being modified by contact with a European coloniser's language. Then sure, English isn't a creole language. But I don't think that's how most people use the term creole colloquially.