Don't get me wrong, I completely agree with you, apart from Harrison and Te'o I think that all of our foreign born players have come through the English system, but the fact that so many were born in foreign countries definitely warrants discussion.
Kvesic shouldn't be included in this argument at all. Just... nope, not event remotely relevant.
I'm not sure that most of the guys you've mentioned warrant much discussion either.
The Vunipolas are both here due to economic migration (AFAIK) and they are both genetic outliers whose father played rugby to an international level - it's hardly surprising that they turned out to be pretty damn good.
Hartley too, was like 14 years old when he moved here with his Mum, and happened to be a very good rugby player. There is very little to discuss, IMHO.
Harrison - moved here for two reasons AFAIK, he was sounded out by Hartley/Saints, who saw him playing for Dylan's old school. And due to a particularly nasty incident that involved the death of one of his friends.
His move here was motivated just as much by non-rugby reasons as it was rugby related ones - he's spent his entire professional/senior career with Saints.
I have no problem with him playing at all.
Te'o, English mum, not tied to another country in this sport - no development by the English system. Fair enough - there are some legit reasons to be upset by his selection, but on balance, I don't have a problem with it.
He also moved away from Straya primarily for personal reasons, like Harrison. I don't see it as any different to any of the players who were born/raised in NZ with Samoan parent/s, playing for Samoa.
No doubt there is a bigger monetary payoff - not even comparible, really, but I think it would take some pretty skewed logic to suggest his motivations are necessarily much different from the "Samoan" players I've mentioned.
Hughes - I and a good number of people on here, do have a problem with his apparently inevitable selection.