Every marketer has a weakness and it's easy to outsource that weakness to a marketing agency. Billy Cina tells it to you straight. It could be in PPC, Inbound, Marketing Operations. That is what you need to outsource to an agency. Keep your strengths in house and take your weaknesses out of the house.
You can argue about exactly what personal branding is, whether it is a thing or isn't but you can't argue about the fact that it's out there. So definitely personal branding is a thing, but putting that aside personal brand is much more than just a fad or just a trend.