Tim Kennedy and Matt Hamil are also much larger than GSP is. not to mention that both guys shot over 10 takedowns and were only able to get him down around 50% of the time. that means he kept getting back UP.
do you really think GSP is going to be able to hold him down with every takedown? the reason i say Bisping has pretty good TDD because he causes scrambles, thus tiring a lot of guys out in the process, which is why he BEAT Matt Hamil, nearly BEAT Chael Sonnen, and drew with Rashad Evans even though they landed quite a few takedowns nobody is really able to hold him down for extended periods.
we're also dealing with an unknown factor. GSP. he hasn't fought in years while Bisping has just executed a giant in Rockhold and avenged his loss to Henderson. ring rust is real and Bisping is a much more dangerous fighter now than he was the last time GSP fought in the UFC.
it's hard for me to believe that he'll just come right in and be the same ol' GSP as before, especially when he was already showing signs of struggling against the likes of Johny Hendricks.