Most electrician here(Canada,Quebec) never ground the outlet itself, because our box are all metals, and the ground is attached to the box only, which is transferred to the switch via the metal frame. But the black paint finish suggest that conductivity for ground is not guaranteed and require additional ground connection.
Electrician still connected the light switch without the ground connection because that what they do… They expect that if they made it of metal, then it can be used as a ground.
I haven’t seen any statement that the metal frame attached with the screw to a metal box(The 2 screw that hold the light switch to the box) can be used as a ground even with the paint on, so maybe it is to comply to the different electrical code, but normally paint mean conductivity is reduced so my personal expectation is that it doesn’t !
So suggestion is either make the switch with no black paint, or confirm that attached screw can still be used as a ground connection if the metal box is grounded.
The only thing that make me think that it might be fine as it is, is the fact that the actual thread of the screw is probably not painted, and the friction of screwing it in would reduce the paint on the thread, so there would be a ground connection from both screw.