My take:
What these three have in common is being Canadian, an influence on music in a shared period in time and excelling in writing their type of music.

Tyson and Lightfood surely had better voices and fresh lyrics (for the time). But,while they were influential, their style of music has evolved into something else..maybe.in another direction. I suspect they are respected as pioneers and song writers. Tyson wrote many songs for other entertainers.

On the otherhand, Cohen had more mystic and his songs are ageless, because of the poetry...much like Dylan. His voice is another matter....some like it others detest it.

Dylan did have a good voice at one time. But, it somehow, or for some reason, got lost (or altered) along the way. There is no comparison betwen Cohen and Dylan in their contribution to music and social movements.

Another influential Canadian of the time was Joni Mitchel, Likely fewer songs, but with a big impact.

I respect them all, their contribution, and have seen each one live...But, not recently.