I love how the logic here seems totally flipped.

"Leveling players in MY leveling dungeon slowing MY run down?! How dare they!"

And Duuude, I think you found almost every possible extreme case to mention, the large majority of which doesn't happen, and with experience in the party, shouldn't happen. So while an interesting counter argument, I'm afraid it doesn't hold much weight.

Lastly, to the experienced players, you were in their shoes once. You WILL be again when Heavensward drops. Remember that.