It’s worse than first class RSVP. Also where I live, it’s a social faux pas to mass invite people to a Whatsapp group as an event invitation for various reasons: it’s annoying, it publishes your invite list, and everyone’s first impression of your event would be a bunch of people leaving, lol. And you probably don’t want a group chat for most events unless it’s a group of friends who already knows each other. Nobody does it.