Warning: Wall of text!

So after playing for about 3 months, I guess I don't particularly get this game. Basically I am the kind of player that over analyzes everything and tries to build the best "team" from the best "units", as it were. So I've looked at Flower Knight unit charts and such and for the life of me, I just don't get the stars.

So when I auto sort Set 1 (Total Power) and Set 2 (ATK high to low) I get 4 teams of knights which are about 90% are the same girls but there are some differences and I don’t get it. Being a typical noob I had a 2 star (Bianca Clover) that I maxed affection on and she’s level 37-ish and she shows up in my 4th Team in Set 2 sitting next to 2 five stars at about 50% affection and mid 40’s…so how is this possible?? How is the system sorting things in such a way that to me, these “lowly” mid lvl 30-ish 2 and 3 star girls are being placed ahead of the 4 and 5 star knights I have?
What is power…and no I don’t mean that philosophically…lol…what’s it based on? I can see 3 things – Actual stats, equipment bonus, and affection bonus. So if I have Knight A with say 1200 ATK with a 100 Affection Bonus and a +600 ring…so…to me…she has 1,900 “power” but what is the system calling her “power”? And why is she “ranked” higher in the sort list than say Knight B who has 1100 ATK, a nice lvl 35 ring +1050, and say a 250 affection bonus (to me she’s at 2,400) she’s considered “less powerful” than girl A because her ATK is lower.
I guess it’s an end game thing that I am not seeing yet because I basically field teams that are mostly 4 and 5 stars with 2 6’s (yes both bought on sale - Cactus thru the developer promo and Alpina thru the 50/50 thing) and some 3’s thrown in but I can’t wrap my head around why I would want to pursue full 6 star sets when I have these random 3’s and 4’s always coming into the mix as “better”. Furthermore, from what I've read the event 5 stars are just..ok?? Are they different than the gatcha 5 stars? I have event girls Holly, Poinsettia, Gaillardia, Pine Tree, and the Star Lily reissue that I've been leveling because...well..they're 5 stars.
Can anyone clarify this? I’d be willing to give specific lineups later because I really feel that I am missing something here and not using units/teams as effectively as I could be and to go back to the first paragraph…I’m an OCD stats guy and a typical glass cannon MMO player so high ATK is generally my priority. At the end of the day do stars even matter???