Although it does seem over powered, there's actually a few ways to fix that:
- Suggested reading: "When you spend an action point to make an attack," might not include having the AP spent to have another make an attack.
- Rules Lawyering: Spend an action point is a Free action (Rules Compendium 235), and you can only use a free action to use an attack power once per turn (Rules Compendium 194)
- House rule: Can only use an action point once per round to most. This brings it on-par with monsters, although the 1/encounter rule for PCs still applies.