> sight is necessary to understand the cosmos

If with sight you mean "capability of elaborating electromagnetic waves in the range of the visible spectrum", the statement is simply wrong. We have just got the report that the first image of a black hole event horizon was taken thanks to observation in the radio-frequencies.

So, no, sight is not strictly necessary to understand the cosmos. It is true that the broader spectrum one can analyze the more information can harvest, but lacking a fraction of the spectrum is no showstopper.

Also on a human scale, several space missions have succeeded in exploring space without having a camera for exploration. Just think of the Sputnik: it didn't have a camera, so technically it was blind.