Whimsicott can actually create many free turns with encore and taunt
Shaymin s has to rely on the opponent to switch out to get a free sub up and the possibility of choice scarf kyogre can really screw u over (don't get me wrong I still think skymin is better due to his offensive presence)
As for hippo, the ability to stall out groudon, as hack mentioned, is very significant, in fact sandstorm, toxic and slack off can take their toll on many pokemon
Which brings me to another point, hippo is the only weather starter with reliable recovery which is just huge
So yes, he's definitely viable
Shaymin s has to rely on the opponent to switch out to get a free sub up and the possibility of choice scarf kyogre can really screw u over (don't get me wrong I still think skymin is better due to his offensive presence)
As for hippo, the ability to stall out groudon, as hack mentioned, is very significant, in fact sandstorm, toxic and slack off can take their toll on many pokemon
Which brings me to another point, hippo is the only weather starter with reliable recovery which is just huge
So yes, he's definitely viable