Yeah I think Suicune would be a better complement to Dragonite due to neutrality to Rock and better overall bulk, but I'm not yet capturing my Suicune in HG so that's going to wait.
I've been trying a team with Whimsicott/Dragonite/Stoutland since I can only use Focus Sash on one Pokemon I tried Sitrus Berry on Stoutland and it is great! I use a Whimsicott set with Taunt/Worry Seed/Charm/Memento but I think using Cotton Spore or Stun Spore would be better than Charm since it would be redundant with Stoutland, but I can't decide which one to use...
I hate Hail Blizzard teams if I can't get enough -Sp.Atk so I'm trying out two cripplers while keeping Stoutland (thanks for opening my eyes on how much of a boss Stoutland is ^_^)
Yeah I think Landorus is too slow to be a set-up sweeper since alot of other stuff is faster than it. Thundurus would be cool but I'm kind of worried that It wouldn't be bulky enough if I can't get enough Charms/Snarls on the enemy.