If an AP tank outDPSes your pure DPS sniper, mara, sorc, DPS jugg, DPS PT, then you need to L2P.
If an AP tank tank to you is sturdier than a full tank of any class in tank gear then you need to L2P.
As for DPS/protection numbers , I do an average 500-700k damage, 200k protection on my AP while my friend guardian does an average of 300-500k damage and 300-500k protection.