So is the purpose of modes to show the link between scales, ie to show and make it easy for us to pick scales that sound right, and to move to different scales. So i should be thinking of soloing in C major(ionain) and then instead of calculating what other scale would sound nice to move to I just think of another mode in C, ed C Dorian or whatever? Is that the point? to move between C modes for a different feel as opposed to staying in that mode.

Thats another thing i dont get, how scales have relative minors, C and A minor, they are modes, ionain and Aelion, how do you know Let it be solo is in C or A minor for example?