As Josh alludes to, TP is not likely to get more than 2.5 million, but not due to the needs of those visitors but the limit on capacity. As much as I like TP, it will always be a gravel pit. Alton Towers was a stately home and grounds, created originally, for one family. The Universal has a blank canvas, with access already being to it's advantage.
It seems I am painting it up, but the better it is, more people will go there and leave Stealth at TP to me.