Affinity is a game mechanic that works exactly as it should.
Except it doesn't. How the MC treats other characters is what would make them see his personality. Things such as offering to help Maya, being nice to Jill, asking Sage how she's doing, should make them as indivduals see him as having a good personality, whereas going the opposite way by not being so nice and friendly to them should make them see him as having more of a bad personality.
The MC taking Quinn's number, or not being nice to Steve, or accepting Jade's advances, isn't forming his personality in the eyes of other characters if the greater sum of his actions with them on a personal level doesn't reflect it. If he was truly a DIK in terms of personality then his niceness would be seen as fake, but we have no indication that anyone thinks that. Even Bella, who doesn't like it when the MC makes the minor +DIK choices, will totally accept a MC with a DIK affinity so long as the status choices with her have been positive.
There's a disparity here between the two different metrics when you have a vast majority of choices being made which directly affect the relationships with certain characters being outweighed by fewer choices that may not accurately the reflect the sum total of those minor choices. It's like if someone were to devote their entire lives to doing good in the world by helping the poor, raising money for charities, giving back to their community, etc, but because they once used an illegal drug in their teenage years that suddenly makes them a bad person and negates everything else they've done. Many of these major choices aren't even all that bad either, so why not being nice to Steve or smoking weed should somehow tip the scale of the MC's personality when he's potentially been a generally good guy is a bit odd.