Whimsicott isn't offensive at all, though. And grass/fairy is a fantastic defensive typing. Yes it has a lot of weaknesses, but it completely resists so many big things. It's weak to elemental attackers, but that's nothing new. It's neutral to fairy, bug and rock. Resists ground, water, dark, fighting. And it's defensive stats are good enough to not take massive damage from these things. Also as the PREMIER Encore user, the more it resists and the more it's immune to the better. Because even if that Conkelldur is carrying Poison Jab, it's not getting the opportunity to use it thanks to Encore.Both Whimsicott and Gardevoir are the sort of lower-tier pokemon that can be perfectly successful in ou, but I'm not sure how the new typing helps whimsicott. Sure it gained an immunity, but one that is usually backed up by fire (and likely now with Steel), two of its weaknesses.
Whimsicott got MASSIVELY buffed this gen from this new typing alone. And if it gets parting shot? It's going to be a momentum-building, neuter-happy machine.