Marauder Archers of Slaanesh should be 90 instead of 120 (Legendary unit size).
CA balancers have a clear pattern. Units of the same type when moving from a melee specialization to a ranged specialization (not counting the ranged specialization with extremely limited ammo) should lose the total number of models in the unit.
I won't bore you with theory, just let me tell you how things are with Norscan Marauders - Norscan melee Marauders (120) turned into Norscan Marauders with Throwing Axes (90) or Darts (90). The same rule should work with Slaanesh Marauders.
Just don't forget to rebalance the unit's stats to reflect the changes. For an example of a rebalance, you can again compare the stats of the Norscan melee and ranged Marauders.