Hmm, not at level 5.
- 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.
- WS is also dual-threat (damage + debuff), while WoF is not.
- 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.
- 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.
- 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.