Blissey & Snorlax Are OverPowered
Two of the greatest Pokemon found in Pokemon GO - outside of the Legendary Pokemon - are Blissey & Snorlax. For one, they are some of the hardest Pokemon to find or obtain. They are also two of the most powerful Pokemon with their extremely high Stamina and Base Defenses. And this is why you see so many people, who are lucky enough to catch or hatch a few of them (Chansey for Blissey), leave it at one of their Team's Gyms. Because of the combination of these two fantastic stats, Blissey and Snorlax both make for excellence Gym Defenders, actually being the two toughest Pokemon to defeat at Gyms. And if they]re at high levels, they're almost impossible to defeat. Thus why so many consider these two species, at least for this game, overpowered in every single regard.
If you ever find or hatch Snorlax, don't even take another second to think about it - Catch it! If you ever have enough Chansey Candy to evolve into a Blissey, take even less time than with Snorlax - Evolve it!