Why is MAX-2SAT not in P?
Observe that the expression ${n\choose k}$ may be exponential in $n$ (e.g. if $k=n/2$).

Factorization is surely in NP. We don't know whether it is in P or not. This is a major open question. The fact that factorization is in BQP gives evidence that it might not be NP-complete (as other NP complete problems are not known to be in BQP)