Digital Audio Workstation (DAW) for people who want to record, edit, mix and master audio and MIDI projects. When you need complete control over your tools, when the limitations of other designs get in the way, when you plan to spend hours or days working on a session, Ardour is there to make things work the way you want them to.
As a professional music composer myself and working on Linux with Ardour, I’d say it is overall pretty good since many years. If you don’t like midi in Ardour you can use another soft to runs midi notes. On Linux the good thing is that if you don’t like something you can change, specially with audio softwares.
To me the two major issues with professional music on Linux are :
Proprietary plugins for virtual instruments are a nightmare (hard to make them to work, expensive on machine’s resources and unreliable),
Most company still think free software = unprofessional/amateur, which can make it harder to get jobs.