The randomness of the centers of your circles is due to the Voronoi randomness. (0 randomness will give you a grid of circles instead.) But the randomness of the individual radii of your circles is due to the Musgrave (which you have set to 3D, but which you’re treating as 1D due to giving it a 1D coordinate.)
If you want perfectly regular, unrandom radii for you circles, replace the Musgrave texture with a Wave texture-- just like you thought about. This will replace those circles with waves.
If you want slightly random radii, perturb the coordinates you send to this wave texture by adding a slight random value to them (ie, a 1D noise fed by the same coordinates.)
But talking about things as being random vs random is not usually very useful. There are a hundred different dimensions of things to be random. Want to make “it” random, whatever it is? Add noise. The trick is, what is “it”?