Number Theory is a tough nut to crack and I feel that, while mathematicians have advanced a lot, there hasn't been any "master theorem" to handle it
Factorization, one way or another, still is done with brute-force (even if it's done in the EC domain or with NFS or related algos). Same for modular logarithm
Most of the theorems still fell like digging a pool with a spoon. Fermat's last theorem was finally proven, with a lot of effort and diversions. It really seems we're missing something "basic" (but complex) about it