Hmm, not at level 5.

  1. Waves of fatigue does have advantages over wearying stance because of the range and likelihood of affecting multiple enemies, but WS is very likely to exhaust a boss or solo opponent in one round; exhaustion is a significant debuff.
  2. WS is also dual-threat (damage + debuff), while WoF is not.
  3. Moreover, a 9th level warblade can spam the WS debuff every round in every combat while still using other potent strikes. A 9th level-level wizzie cannot spam WoF while simultaneously throwing other mainline spells.
  4. Also, the 30-foot range on WoF is a significant limitation on the spell, since the typical wizzie debuffer is squishy and desires to avoid melee. The fact that WS is Range: Thwack is no concern at all for the typical martial adept, who prefers to be adjacent to his foes.
  5. Further, WS scales better with level than WoF, since it grows more effective as the adept gains more attacks per round and a higher attack bonus.

If WS were to stack with itself, I'd place it at 6th level.