Wailord is pretty much completely outclassed by other Waters, while Walrein stands out a bit more with a better movepool, typing, and stats. They're both still far from the greatest Water-types by your criteria, such as Pelipper and Swampert.
Spheal
Availability: Late
Stats: Above Average
Movepool: Decent
Additional Comments: He comes late, but Water/Ice is a good STAB combo and Walrein is very bulky with decent offensive capabilities.
Wailmer
Availability: Mid-game
Stats: Average
Movepool: Shallow
Additional Comments: It is slow, not overly strong, and by time you can get it you have already seen too many other good options for a strong Water-type.
Also, as Fizz said:
The main reason you shouldn't use Wailord is that it has Fluctuating growth rate, which makes it a terrible experience leech.
While Spheal has a better "Medium-Slow" growth rate.
Hope I helped!
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