To be fair, Wailord's problems are more than just Keldeo outclassing it, since there's no Keldeo in UU or RU but it's still rubbish there. But that's neither here nor there.
As for Wailmer, in terms of viability, it's one of the lowest ranked Pokemon in the tier, and is a niche Pokemon at best. It's true that Wailord is on the high end of the special attack spectrum as far as water types are concerned in LC, and can make a decent cleaner late game with its Scarf set, I won't debate that. Other Water types just bring more to the table. It's worth noting that it finds competition from Remoraid, who despite having marginally lower SpA (16), manages to reach 17 speed, also boasts Water Spout, but also packs Fire Blast and can run a mixed set with Hustle Bullet Seed to break through other water types. Chinchou deals with other water types better due to its electric typing, granting it better coverage in general despite lower power, and it reaches the same speed tier (16 unboosted) on its Scarf sets. It also is able to run better defensive sets as well, and access to Volt Absorb allows it to better check not only itself but things like Staryu as well. Staryu's got a better base speed tier, packs Thunderbolt to beat other Water types (well, barring Chinchou of course), isn't screwed by paralysis thanks to , and has a bit more versatility thanks to Rapid Spin and Recover. Omanyte, Shellder, and Tirtugo can all run Shell Smash sets, and there's a whole host of water types running physical sets in LC that Wailmer doesn't try to compete with, such as Shellder, Carvanha, and Corphish. Wailmer's niche is, was, and always will be Water Spout, but it's a small niche and outside of it, it doesn't have a lot else to differentiate itself from the competition; even non-water types have a lot of popular Scarfers that can clean up late-game, and don't have their strongest STAB get neutered by prior damage. It does have respectable power on Surf or Hydro Pump, (I prefer Hydro Pump because Surf can miss the 2HKO on things like Pawniard), but the power is more comparable to other threats. Water Spout is how it differentiates itself, albeit in a high-risk, high-reward sort of way.
I'd question your set in a few ways though. For instance...
ger9119 said:
EVs: 36 Atk / 236 SpA / 236 Spe
Mild Nature
...Is inefficient because almost all of those EVs are wasted. On a Mild Wailmer, 196 EVs will maximize its speed, and even then, it only hits 15 speed, which in turn causes it to be outsped by Scarf Chinchou (who reaches 16 speed unboosted even with Modest) who can soundly 1HKO Wailmer with Thunderbolt, while Earthquake fails to 1HKO Chinchou, even only having about a 6% chance to do so with Stealth Rock up. This set, reaching only 15 speed, which equates to 22 with Scarf, causes it to be outsped by most boosted Pokemon, such as the infamous shell smashers of LC, all of which barring Tirtuga outspeed it, and even then your set only speed ties with Tirtuga after the Smash.
The SpA EVs also fall flat as well. Anything over 200 is wasted, 17 is as high as it's gonna go and it reaches that at 200 EVs. You also need 40 attack EVs to hit 14 attack, which is necessary to be able to have a shot at reliably 1HKOing Chinchou, given that with rocks at 14 attack, you bump that 6% chance up to about 56%.
Now, if you do want to run a mixed Scarf on Wailmer, most notably to be able to beat Croagunk which Special sets aren't really capable of doing (since HP Grass can 2HKO Chinchou on special sets), it'd end up looking more like 36 HP / 40 Atk / 200 SpA / 196 Spe. This'll get you that 14 attack, 17 SpA, and 15 speed that you need to maximize output on a mixed set. That said, I'd still prefer Timid on a Scarf set for its ability to reach 16 speed. But that's just me.
