Totally agree. Not sure what tiers you're going off though. Toxicroak, Jolteon, Chansey and Deoxys-D are all OU on Smogon tiers, but Roserade is OU on PO tiersHonestly, there is almost no reason to use Arcanine over Darmanitan. They have the same speed stat, but Darmanitan has Sheer Force. My damage calculator is down, (WHICH IS A BIG DEAL) but I assure you that it 2HKOs Jellicent, Tentacruel, Latias, Gliscor and Dragonite, plus maybe Slowbro with Sheer Force Flare Blitz in Sun. It also has Earthquake, and U-TURN, which is huge (U-Turn easily does 60% to Ttar and takes a ton off of Toed). Hell, it can 2HKO offensive Rotom-W with Fire Punch in the sun.
Darmanitan @Choice Scarf
252 Att/ 252 Spd, Adamant/Jolly, Sheer Force
So I looked at the Pokemon that do not receive enough usage to be OU (included BLs, which after all are used just as little as UU pokes), and here is the Superstar ranking of the top 10 usefulness in OU:
Got a weakness to boosting sweepers? Need SR? Have a weakness to Dragonite, Heatran, or Tornadus-T? Ditto can revenge kill all these threats and provide a ton of roles on the team. Honestly, I hope it stays in NU, because it's great in every tier its allowed in.
How is this BL? Everyone knows who it is and what it does.
Yeah, it's slow. Yeah, it's tough to get in. But once it is in, something is going to die. Hydregion can 2HKO every single Pokemon in the game bar Lugia and Physically Defensive Steel Arceus in Rain with a set of Life Orb, Superpower, Fire Blast, Draco Meteor, and Earthquake -- and they aren't in OU, are they? Honestly, if it weren't for Genesect, Hydregion would easily be OU.
Everyone knows who Wobbefett is and what he does. Revenges with 100% reliability almost all Choice users. I can't think of a comparable OU example, but in Ubers I would start to sweep with Darkrai. Darkrai would then die to a Choice Scarf user. Wobb takes out the Choice Scarf user, which removes their only Mewtwo check, gg. Stuff like that in OU abounds.
Walling almost all physical threats in the game, including Terrakion? Sounds good to me. Slowbro is a great Pokemon, and honestly if he got SR and Amoonguss got Spikes, stall would suddenly be viable in this metagame.
With rain predominating, Azumarill becomes a great Pokemon who can revenge a large portion of the metagame with STAB Aqua Jet, including all the Therians, Landorus, Volcarona, Terrakion, and Genesect
Zapdos is pretty underrated, serving as a great check to Tornadus-T. Once Lightning Rod is released, I will use him on every rain team I have. STAB Thunder off that SpAtt stat with that bulk is pretty nice too. Unfortunately, Game Freak gave Uno and Tres Hurricane and forgot about Dos. Come on, give number two some love.
The face of sun offence gets a nod over Darmanitan because he is almost as powerful with V-Create, reaches the all important base 100 speed stat, and still has U-Turn.
He's lean, mean, and fast. By outspeeding everything in Sand and still hitting hard with Choice Band, Stoutland carves a good niche in the OU metagame. His only problem is that he is weak to Mach Punch, and Normal STAB sucks.
10 - Kingdra
Yeah, he's outclassed by many other Dragons, but he's not weak to Ice Shard and can OHKO Mamoswine. He can survive pretty much any priority attack, in fact. And once rain comes, look out! He all of a sudden became a fast, powerful sweeper immune to revenge killing by the likes of Genesect or Scarf Terrakion.
Just missed the cut: Bronzong, Jolteon, Chansey, Xatu, Toxicroak, Sabelye, Kyurem (outclassed by -B), Roserade, Darmanitan, Amoonguss, Gothitelle, Chandelure, Cofagarius, Feraligatr, Weavile, Aerodactyl, Sawsbuck, Lilligant