>>19053877Charizard is powerful, has good abilities, movepool, and the unpredictable factor.
Venusaur has good bulk, resistances, and few weaknesses for a grass type, one of which is uncommon.
Blastoise is just one of the many bulky waters. The only diference is that he has rapid spin and a way to effectively kill ghosts. Also, aqua ring is the only recovery, but will never recover nearly as much as roost or synthesis do, lack of a secondary typing is also bad. Charizard has dragon and flying depending on which mega, both good offensively, venusaur has poison which is good defensively, and blastoise just kept waiting on a steel typing but got unlucky.