IMHO, your concern at the time of installation is that you do not exceed the rating of the device controling the load.
The circuit is protected by the 20 amp OCP, which is compliant.
For example; you install 6 recess fixtures with 75 watt lamps, totaling 450 watts. The load on the device is within spec, even if it is two ganged.
Some time after you do the above; someone replaces the lamps with 150 watt lamps! The dimmer takes the bullet!!
Code compliance is 'at the time of installation/inspection'. There is no crystal ball, no lady reading the future, and the NEC is not 'idiot proof'.
A 120 volt 20 amp circuit calcs to 2400 watts, max load for non-continuous, and would be compliant. Common trade practice is NOT to load any circuit to 'max'.