Victimize deals piercing damage. (It says so in the tool-tip, at least.)

The reason your Victimize does so much more than your Doomspike is because of the crit attack power materia you have in your (exclusive) Pugilist body.

The reason people say Doomspike is better than Victimize is because Doomspike can be used 1.5x to 2x more than Victimize.

This isn't as much of an issue on "raid" fights like the Deepvoid Slave and Batraal because there are still ways to get evades/misses while in a DD role.