I'd have to disagree. He does really good damage - the trick is to never have him get a kill so his HP never resets.
Full disclosure: these images are from tier 4 and 5 raids. My guild is nowhere near heroic level, so ymmv.
I like him best in phase 2. Sion's pain on himself counts as a debuff, so Death Panda always has advantage (except after special). Kylo's AoE then feeds him 50% tm (almost) every time. Also, KRU's basic triggers his taunt when Sion has pain on himself, so helps keep everyone alive. Yoda just for damage buff on panda. He's not super critical, but still helps to keep FOO alive later on.
Edit; I have a fully maxed (g12, 3/6, zeta) FOTP, and death panda out scores him every time. Panda is 6*, G11 5/6