The exact numbers would be difficult to calculate and I won’t get into that. However your speculation is right that the odds favor the dealer if he leaves a lot of high cards in the discard rack yet will put back into play a lot of small cards. This would be the same kind of thing as preferential shuffling, in which the dealer of a hand held game shuffles when the count is good but deals another round on a bad count. Preferential shuffling is something that definitely does happen here in Las Vegas so what you describe would not surprise me either.