Is Cloyster more effective against a Dragonite than a Lapras?

Does a Cloyster fare better against a Dragonite than a Lapras, or even a Dewgong, does?

On the Gameinfo site, it claims that Cloyster is 100% effective when fighting a Dragonite, while a Lapras has a score of 94%. Dewgong has an effectiveness rating of 80%. (All of them have Frost Breath and Blizzard and all three Pokemons have the type Water / Ice). Why does Cloyster work better than a Lapras or a Dewgong?

In practice, I find Cloyster dying quite soon due to its low HP. Dewgong even works better than Cloyster, but Lapras is best due to its high HP.

Solution 1:

From personal experience (and it sound like yours, too), Cloyster does not fare as well against Dragonite as a Lapras does. In fact, before Training was fixed so you could have 6 Pokémon and the levels of the defenders was scaled to your own, my ~1950 CP Lapras defeated a ~2400 and ~2600 CP Dragonite in one go. I can assure you my Cloyster would not have lasted that fight.

Looking at the page, the only reason I could see them giving Cloyster a higher "effectiveness" rating is that Cloyster has higher ATK and DEF. This assumes the calculation is completely ignoring STA, since Lapras absolutely dominates in that regard.