Hi and welcome to Arturia forums.
Be careful not to take pitch as a waveform width in the sense we talk about here, as different pitches have different widths. What we talk about is the width or shape of a waveform in any pitch.
In the waveform display you can see the Width parameter for the triangle actually is controlling the shape of the waveform between a triangle and almost a ramp up saw.
(I think the way it's pictured in the display indicate the reset phase of the waveform.)For the Square the Width parameter create different Pulsewidths waveforms, and this is the original pulsewidth setting possibility.
As the Width parameter is applied to change the Triangle waveform, then i can't tell, why there is'nt this feature for the Saw and the Sine waveforms, as there could be. One can say that the Saw perhaps would be the opposite of how the Triangle Width works now going from a ramp down Saw to a Triangle. And the Sine could also get some kind of shape changes too. Perhaps there are technical reasons. Or Arturia may have decided that this is covered by the width settings you can set for the triangle and the Square waveforms.
If you modulate a Square waveform, then you get pulsewidth modulation.
More info here:
https://en.wikipedia.org/wiki/Pulse-width_modulationThere are much info out there about this.
Hope this helps.