You are assuming that (some/most/all) these problems are caused by the new solder. For that fraction of problems that were, perhaps they are just teething problems, and, those problems have been solved?
But, I fail to see how you can blame solder for inadequate cooling engendered by a desire for excessive thinness and some particular aesthetic look? Perhaps Apple needs to point some of its engineering resources towards doing some cooling analysis aerodynamics?
Both.
http://www.ecnmag.com/article/2011/12/was-lead-free-solder-worth-effort