You can spam a move with the same base power as Hurricane, that doesn't mean that its a good move to spam.. Hurricane is resisted by rock, steel, and electric. Electric pokemon aren't very bulky and hardly present in OU. SDef Rotom tries to be, but gets worn down over time. Rock and steel are weak to Focus Blast/Superpower/Heat Wave in the case of Tornadus-T. Thunder is resisted by Electric, Grass and Dragon. It also does zero damage to Ground and heals Volt Absorbers, boosts Lightningrod users and even boosts Cell Batter users(even though no one would use it). Your secondary option is HP Ice. It isn't scoring you any KOs on grass types as it sucks and grass types in OU have bulk. It isn't even SE against Electric, so that's a waste. So does it help against dragons? Well.. Dragonite has Multiscale+Espeed, Mence is always scarfed or +1, Lati@s lols at it, Garchomp outspeeds and comes out with zero damage if switched in on Thunder, and Kyurem-B+Kingdra don't care about HP Ice. Meh..... why is it that I can come up with a thousand ways to deal with something everyone thinks is a threat? Edit: Oh and Umbreon IS better than Chansey/Blissey. They have no offensive presence and mediocre support options. 350 HP wishes are overrated, that's like the average TOTAL HP for a Pokemon. What are you going to switch in your 1 HP Pokemon in on an obvious attack? Thunder Wave is decent, but hogs a moveslot. Toxic is bad in this fast-paced meta and Seismic Toss is a joke. Umbreon has Foul Play and Payback. The first of which usually doing a very nice hunk of damage. Synchronize is a great counter to status moves, IMO better than Natural Cure. Plus dat Heal Bell. Umbreon's typing actually gives it 2 resistances and an immunity for more switch-in potential. It has the benefit of having leftovers recovery and not being obliterated on the physical side. It just all around is a much nicer option.