What do I know… but perhaps the effects of mass items on the ground on top of each other is far worse than items that generate in individual squares in the trees… When fruit falls, you have the combined apples (all apples from a certain vertical column) stacking on top of each other on the ground. Add to this (in the dodo farm scenario) dodos walking across and eggs laid in those same spaces and I would think there is much more data/activity in each of those squares that may cause the compounded lag.
I also think there is no questioning the fact that the 1.7 update generates larger mobs. Dodos hatch like never before. As do all other animals. I mean… the shark numbers are bonkers. To me the increased numbers are really noticeable (dodos, sharks, donkeys – drop bears seemed to stay the same, scorpions seemed to stay the same, fish seemed to stay the same… and there is, of course, the addition of unicorns as well).
When I was on MR last with Wicked only, the lag on my server was severe. I had a hard time just placing signs. Ended up having to have Wicked leave for a time while I did it.