Well, I doubt his 2006 is much newer than my 2007 model Rockwood.
And as I stated, how is a 2" ball unsafe? Too small? 5/16" bigger is that much safer? What do you base this on? Size alone? So a 2000# rated 2" ball is the same strength as a 2" ball rated at 10,000#s?
Silly Rockwood for putting that 2" hitch on my TT!
Rather go by a subjective comment, I'd suggest he take a look at his GVWR, then pick a ball with the proper weight rating. Think you'll find both of the ones I mentioned are well over his GVWR...
If the coupler on his new trailer is like the one on my new trailer, I'll be curious to see how he's going to make a larger ball fit. As I said, there's no adjustment on the underjaw, so only a 2" ball will fit unless the coupler is cut off, and a new one welded on.
He asked if it matters what size ball he can use on his trailer... and the answer is YES. A 2 5/16" won't fit on mine. Yours doesn't even have a ball, so I suspect that's why your answer differs from mine. On some trailers with an adjustable underjaw, such as my old Popup camper, I could tweak this:
But as usual, YMMV.