A little from column A, a little from column B. I get the point of isolation exercises to work a particular part of the body, but I think and have read that whole body exercises develop overall strength and balance better than isolation exercises.
I'm going to start working on deadlifts but I've spent time doing back raises so my back is kind of strong. I do find it is the weak point in my squatting since I fear blowing out a disc so I take it easier on squats than I could.
Also, Sapphy, adequate rest the night after a workout is essential to helping your body recover and build muscle.