I know this is an old post but I thought I would explain what's going on. The learnsets on Smogon do not include event moves, which includes XD purification. In addition, the only moves listed in each generation are those that can be learned in that generation. To see an example, look up the gen 5 Stealth Rock page. You'll see a lot of missing Pokemon! I don't think Chansey is going to be enough to make stall viable in UU. Umbreon and Snorlax are similar Pokemon, albeit much less bulky, and they don't seem to be making stall particularly dominant. With the addition of Eviolite since Gen 4, Chansey will be nuts, but stall's problem was never that we didn't have enough special walls.