Its the GFCI outlet in the garage that makes it such a pain. You did not need a GFCI breaker because the power with a regular switch was either on or off. Smart switches do not fully turn off the power to the devices the control, the just limit the current. Using a smart switch instead of a dimmer may work, but Lutron never chimed in to say if the Caseta smart switches are listed for control of a GFCI outlet, its probably not because of the 6 amp limitation.
A regular switch handles the current and the heat better because it is just a simple physical connection that is open or closed. For any smart switch to work power needs to flow through it, the more power that flows the more heat that is generated, the larger the components need to be and so on. Since most items use less than 6 amps it is normally a non issue. The problem comes when you have an outlet that could be used for anything...
Moving the GFCI protection to the breaker is better since we know the outlets will be GFCI protected and we know the GFCI device will not be effected by the smart switch.