> There are enough similarities to give them significant advantages compared to immigrants coming from other parts of the language tree.

Depends which other parts. Disadvantaged compared to German or Dutch speakers, and even French speakers, but, sure, advantages compared to other, say, people whose only prior language is Mandarin. And, of course, a big disadvantage compared to immigrants who already speak English, even if it's not American English.

But still very far from starting off even functional, much less halfway to native fluency.