This whole icing issue has me doing research. One idea I'm tracking is the amount of water in egg whites. It seems the older the egg gets, the more the whites convert to water. I wonder if the original Sweetapolita author used very fresh (read: expensive) eggs? It doesn't seem as though size makes a difference (large versus medium); the water ratio is still the same. But...when I was doing various tests for my library pastry cream and lemon curd classes, I noticed the cheaper "store brand LARGE" eggs were slightly smaller and weighed less than the "just laid" large eggs I get JUST FOR ME from a local farm. That meant in my instructions, where I gave weights, I also had to give a range of eggs necessary to get to that weight.
A corollary to the water issue: I think butter is having more water added to it. It seems to take longer to make reduce butter to make ghee than it used to.
Anyway...to my mind (always a tricky place to wander around in) the water amount comes down to "less egg white protein >> less strength for the whipped egg whites."
More to follow. I'm trying to decide which recipe to make to test this idea. Looking for the smallest amount of icing I can make to verify...anything.