Well, all I can say is that if you ask 10 Schluter guys about Schluter products and they'll all say the same thing; if you ask 10 tile guys about Schluter products in a tiled shower, you'll probably get a 50;50 split. If you ask about Kerdi products in a tiled Ontario shower system - if you can find 10 of those - you'll also get a mixture of answers.
The fact is debatable and it is far too early in the existence of "Kerdi showers in Ontario" to be able to say what the right way is; but one thing Kerdi won't tell you about is how we here in Canada like to have our showers dry to the interior and we use Kerdi because it is (a) waterproof and (b) a vapour retarder. If you are worried that the small amount of vapour getting passed the Kerdi, the cbu and the vapour barrier, then by all means keep the vb
intact. IMO there is greater evaporation 'draw' of vapour to the inside of a 20deg C house in winter than there is tendency for that same vapour to exit via the wall cavity.
But that's just me....