I've worked on both as corporate IT and MSP owner. There is a place for corporate IT and a place for an MSP.

The MSP was the clear winner in small companies. Someone trying to do dual roles such as IT and accounting was generally weak in one or the other because they weren't spending enough time on one or the other to become really good at it.

On the corporate side, even if they hired lots of stuff out, they still needed an IT Manager to manage all the IT projects. They knew what was a priority for their business and managed projects accordingly.