I'm going to get crucified for this, but paid advertising is somewhat analogous to software engineering/developers. There are many languages/platforms/technologies out there. Some old, some cutting edge. Each one most likely has it's own syntax/terminology, patterns, approaches etc.
So when hiring a full stack engineer, you look for someone who cuts pretty deep across a few key areas, but can also roll up their sleeves across the stack if need be. Example: Ruby Expert, Getting into Angular, and knows how to provision AWS if need be.
Same thing with full stack marketer. If you know Google Adwords, Content Marketing and a bit of PR are your core, then optimize your hire for that.