Some questions came up in regards to STR, Lifting and PL levels. I tried to explain, but then myself got confused and was unable to answer the questions. I knew this forum was the best place to get the answers. I appreciate any and all responses to help clear up these questions.

The questions surrounded Power Girl (PG PL, 13 STR 17, Lift 21), Mary Marvel (MM PL14, STR 17, Lift 21) and Wonder Woman (WW PL 15, STR 16, Lift 22).
1) Why is WW a 15 PL, MM at 14 and PG at 13? What makes them be at those levels? How can one tell what PL level a character should be? For example, both PG and MM have as many powers or more than WW, yet WW has a higher PL.
2) If WW has a higher PL, how can she have less STR? I tried to explain that STR was punching power, Lift was the amount of weight one can lift and PL has to do with overall power, but then I wasn't sure if that was all correct. Also, if one is weaker, how can they be more powerful overall when the other 2 also have many superpowers? I was at a loss here. (I mean I understand that a character could be physically weaker but have super-energy powers or super-speed or something which would raise their PL above another with superior strength, but in this case with 3 very similar ladies, it was confusing).
One friend wondered if they could all be seen as equal in regards to STR in terms of STR+Lift. For instance, if the three of them fought, wouldn't they all just be equal in terms of the STR-LIFT (not fighting ability)? PG and MM are 1 above WW in STR and WW is 1 above PG and MM in Lift. I wasn't sure they were equal or that they equal out in this way (17+21=38 = 16+22=38)??
The other friend thought maybe the listings were such to show strong Kryptonian females (PG) and females with magical bodies (MM) were Stronger than even the strongest female (WW) and the rankings were done in this way to keep everything ordered throughout the system. Sort of the way Superman (strong male Kryptonian) and Captain Marvel (male magical body) were stronger than Mon-EL who is a Daxamite strong male. But Mon-El's PL is 2 below Supes and CM and he cannot lift more than those 2 can, so that didn't really fit so well as an explanation.
I Hope these questions are clearly written and I appreciate any insight into them.