Complaining about the unresolved romance is missing the point.
For both Mai and Reika, Kunimitsu was their purpose for playing soccer. Mai had mixed motivations for joining the team, but she convinced herself that she'll only win his attention by playing. Reika flat out states that Kunimitsu is the only reason she's playing soccer.
The whole story of Mai Ball is Mai moving past this and falling in love with soccer for its own sake, between the relationships she builds within Kijikita and seeing soccer from different perspectives through her opponents. Mai's character development culminates with her realizing this, confessing to Kunimitsu, and playing at her peak skill level against Mia without relying on her fantasies to keep her distanced from the game.
Now, a year later, both Mai and Reika continue to lead Kijikita. Mai loves the game, regardless of her relationship with Kunimitsu. Reika still claims Kunimitsu is her focus, but she's making up elaborate conditions not to settle the issue. We can infer that she also simply loves soccer too but is too proud or stubborn to realize/admit it.
Mai "winning" Kunimisu isn't important compared to her growing beyond that one goal to love soccer, which we see fulfilled in the story.