SOL increases energy attack (not by much).
Focus increases Hitrate (1 foc = 10hr). Is needed in higher levels because hitrate/focus of namekians sucks.
Well i guess no one uses stats like STR or SOL. They are not needed and won't increase your damage much. As a DW get a lot of focus on gloves because if u miss u will lose aggro (crit % is not bad either on sub weapon).