I would eliminate part (a)-- is it really necessary? Seems a bit arbitrary. But the main thing that I agree with here is, the very idea of having a designation called "Major planet". That's the crucial factor here-- the IAU basically uses the word "planet" when they actually mean "major planet". Please do carry on with your plans to email this idea, and stress the importance of having the "major planet" designation, regardless of its attributes. That pretty much solves the problems in one fell swoop, and allows for a much more inclusive definition of "planet", which is the key element.

Also, while you're at it, I recommend you also include a new category, called "satellite planet". I really hate this idea that a moon can't be a planet. When you look at Titan, and Io, etc., and study what is going on with these objects, it is very tempting to make comparisons to Earth. That's called "comparative planetology", but you wouldn't do it unless at some level, they were all planets! To borrow Ronald Brak's apt analogy, you wouldn't do "comparative fishology" between a halibut and a dog, but you certainly would between a halibut and a trout. It wouldn't matter that one was in the ocean and the other in streams, they are clearly both fish if you put them on the table and give them a good looking over. A planet by any other name... will just devalue obviously appropriate comparisons. This will become paramountly clear if and when the search for life on "other planets" begins in earnest in the next few decades.