EMT for ground relies on
- Scratching the paint off, adequately, from breaker panels or other painted boxes to which it is attached,
- Set screws being tight, rust-free, etc.
- the system remaining intact over the long term,
- naive homeowners and handipersons not replacing it with PVC here and there,
For those reasons some electricians regard ground wires as more reliable. Others go by code and rely on the process by which code is written (X causes harm, stop doing X) to guide them. I think the smartest thing is to not get between these people. :)
Sometimes a ground wire will push conduit fill over the edge ... in those cases that should be the deciding factor, especially if the conduit is already in place. But again, some electricians would say this should be the trigger for bigger conduit.
As a DIY-er you might want to go with ground wires simply because paint-scratching is a bit of an art and there's no easy and reliable way to test it. Professionals know they are doing it right because they have practice. At least if one end of a conduit is in a painted box, you could run a wire there.
My guess is that in a house where the homeowner is aware of this question and thinking about it, the worries about EMT are already much less. You can mitigate the risks (if there really are any) a lot just by inspecting it.