Those stats indirectly help combat by allowing you to advance through your real-world relationships, which unlock different abilities and combat moves as you level the relationships up. I don't think it's possible to max everybody out as there are a lot of playable and non-playable characters that want to spend time with you at different stages in the game. So you might want to look up who provides what abilities and plan your time wisely.
FWIW, this game nearly killed video games for me. 120+ hours to complete a fairly linear single player game (and I don't feel like I was spending an excessive amount of time doing side quests and stuff) was just too much. The only thing that kept me going was the combat, which I really enjoyed. But there are blocks of hours where you are trapped in dialogue loops and the only breaks you get are when you're standing in your bedroom, and literally your only two options are to save the game or go to bed (which starts the next day into dialogue ).
I had to take a break from games for a few months after I beat P5.