And how are you attaching/securing the panel? The "bumps" are part of the panel.
And since you 'know' this to be true would you please show the inspector this?
Just about all type 3R enclosures have the "bumps", or mounting feet that space the equipment from the mounting surface. What you suspect the reasoning is for them to provide this, when they probably could save a little in production costs by not doing that?
Why does everyone think masnory walls are wet or damp locations? Some are. But not all are. Does a piece of plywood whether painted or treated change that? The moisture is still there, if the wall is continuously wet the plywood eventually soaks up enough conditions will be worse than mounting the equipment directly to the masonry wall.
I usually only mount panels on wood like that if the masonry wall is in poor enough condition that it will be difficult to successfully attach the panel or if the surface is so uneven that it will be difficult to successfully attach the panel.
If the masonry is excessively damp the panel is not attaching to it and neither is any absorbant backing.