As a player in campaigns with Rogues, I have seen the overconfident Rogue Tumble into battle, sneak attack and kill someone, and promptly get tarred by the target's buddies. It is a much harder proposition than you may think.
As a DM, I take inordinate pleasure in tarring the overconfident Rogue that Tumbles into the middle of an enemy formation.
Trust me. Your AC will NOT save you if 2 or 3 guys get off 2 hits each on you that round. A level 20 Rogue has, on average, 70 hps. Add 60 for Con, and you have 130 hps. A CR 16 monster will get through that in 2 seconds flat, let alone 6....