3k TP Simian Thrash hits significantly harder than 3k TP Victimize (with multiple enfeebs on the enemy as well). This has been true since the 2nd damage buff for Simian Thrash. Tested multiple times against multiple mobs.
The ONLY WS I imagine may match or overpower a 3k TP Simian Thrash at this time is a 3k TP Chaos Thrust done when the target is under 20% HP.
Only WS ARC has that may do more damage is Bloodletter - which only holds true against targets with naturally high defensen so that the static 500 damage at the end of the dot makes it no contest.