It's not like he will be any less influential where it matters. Merely running a company probably isn't Musk's most valuable contribution to Tesla. This will give him more ability to focus on engineering matters.
There are comments about how quickly Musk managed to understand rocketry but that doesn't make him an engineer. I suppose he has enough knowledge to understand what SpaceX is doing and where to invest but not for designing entire rockets.
Nobody knows as much about every single part of the Falcon 9 as Elon. Again, this has been said by many people.
Please actually inform yourself and don't be guided by bias.
[1] You could argue it's true by pointing out that ninety percent of Tesla's marketing IS engineering, engineering that fuels a powerful perpetual hype machine.
[2] It's obviously not. He is formally trained in economics and physics, and he proved these qualifications with PayPal and SpaceX respectively. When it comes to marketing he's quite clearly uncomfortable in that role.
But Musk does a thousand times more engineering than I do. And he knows a thousand times more about engineering than me. Or anyone of my colleagues.
He can surely also be considered an engineer.