I don't think I'm ever going to agree that a 100mm waist is needed/desirable for EC tree skiing. Actually, it's the honking wide shovels that I don't like (anything wider than around 125 is too wide, IMHO). If the width of your skis makes a narrow bump line seem crowded, then I think they're too wide. My opinion.
Instead of arguing about width (a waist of time), there is one attribute of a good EC tree ski that I would like to add to this discussion. A big upturn on the tip (prime example is the K2 PE/Extreme) is a valuable attribute/quality in an EC tree ski. Why? Because it generally causes you to go OVER that tree stump, or branch, or whatevever, that you didn't see, partially buried, under the snow. I'm not sure that tip rocker (which has a more gradual rise over a longer distance) provides the same benefit. I think "extreme powder" rocker would have the same effect, but I don't think "marketing rocker" would.