TRY It, get an incandescent bulb and run it from PWM get warm and is dim red, hotter get orange and full power glows white. That is what PWM is for.
True triac turn off when current goes to zero.
So integrate the PWW to some voltage that turns triac on at same phase angle on each cycle and you have nice smooth power control.
From my experience of Solid State Relays you use them like mechanical relays to just turn on and off.
But dimmers that use triacs integrate the PWM into a voltage that triggers the triac at same part of phase angle on each cycle of the mains hence you get nice smooth power control