the theories on here were actually more creative and interesting than the ideas that were actually explored in the finale

The finale left me pretty dissapointed to be honest, although having more substance than RTD's finales it didn't really pack a punch!

I kind of wish some of the ideas on here had been the finale instead!

It was ever thus

Yep, the basic plot structure of the finale has to include elements not already present in the rest of the series. You're never going to be able to extrapolate the whole plot from previous plots...