I will give my honest opinions about the series having watched and wait for 2 seasons. Quality wise, I believe Season 1 had better cinematographic effects + it felt easier to watch while Season 2 made used of more visual cues & was a more serious tone? Also, it didn't help that it took 2 years for the next Season to be launched and I felt kind of disconnected from the first season already.
While watching Season 1, I was Team Hyeyoung, but of course we can deny the chemistry Jojo shared with Sunoh. However, I just wished that they provided more explanations to justify the relationships and actions of the leads. Just some points I would like to point out which I felt awkward:
- so why did Jojo left Sunoh in the first place ? why did she install the shield for him?
- did i miss something, because it's suddenly Gul-mi & aunt were suddenly caring for her?
- so Jojo ended up with Hyeyoung alr since start of S2? How?
- what's Dukgu back story + Brian Cho involvement --> i get some ending cues from this, but was hoping for more explanations
- so Sunoh just suddenly goes for Yukjo now?

Regardless of the loop holes, I believe it was realistic for Jojo to end up with Hyeyoung and here's how I intepreted.

If the notion was right, at the end of S2, Dukgu mentioned that people becoming increasingly reliant on this app that may not actually be true representation of their heart? It is actually evident, since Hyeyoung was the true inspiration of Love Alarm app? He loved Jojo secretly, even before the presence of the app, Probably it mimicked Dukgu's inner feelings of loving, but without a courage to confess, which was why the app was created. In S1, i actually felt awkward for Sunoh & Jojo to fall so quickly for each other, but I won't say it is entirely wrong. It just felt like the relationship blossomed purely because they complete opposites + Sunoh was direct and straightforward and of course ringing her alarm. However, Jojo was self-conscious and insecure of course due to her childhood trauma. She has fear of loving someone, because it also meant sharing insecurities with the other person + possible abandonment. Probably more so it didn't help that Sunoh was of a higher status, which made her wanted to hide herself more and of course doubt herself whether she deserved such feelings. Its also proabbly why she wanted a shield as she didn't want to get hurt. Hyeyoung on the other end, was patient and was willing to wait. He didn't place pressure on Jojo with his feelings. He placed Jojo's feelings & well-being before anyone's and made her realize she is a person worthy of love. He was also the person who taught Jojo what love was and that feelings itself makes one stronger and not vulnerable. Which was also the reason why Jojo had wanted to remove the shield later on.

If you think about it, Jojo had feelings for both people. However, it's probably Hyeyoung who made her want to be a better person. Sunoh on the other hand loved her, but made her more insecure since she was already struggling with her self-issues. Ultimately, it made as it seems that the app itself had made people forgot how to love themselves first, before loving someone else. It was also because of this app that people are having less control of their feelings and volatition. I just felt that maybe all these were not well-portrayed through out season 2, which was why viewers are left confused. It would have been better if more explanations had been made on Jojo's actions/decisions. In all, I am just happy Jojo and Hyeyoung finally found each other with/without the app :)