I find it interesting how the OTP of Nice Guy contrasts with the OTPs in the other three currently airing kdramas that I am following - Faith, Arang and the Magistrate and Five Fingers.
Because in the latter three, the OTP make each other better, they are functional together and their obstacles are external. It's most visible in Five Fingers, where Dami is Ji Ho's beacon of sanity, and that is why they must be forced to break up - otherwise he'd never descend into darkness necessary for revenge. You can watch only a few minutes of Eun Soo/Choi Young of Faith or Eun Oh/Arang of Arang to see how incredibly functional and functioning they are together. And the obstacles all the couples face, while huge (and possibly insurmountable) don't come from their intrinsic natures and flaws but outside forces. If these outside forces went away, you just know nothing would block their happiness - Eun Soo and Choi Young have the huge issue that she is a 21st-century woman and he is a 14th-century man and neither can live in the other's world. Not to mention an awful lot of people are trying to kill one or both of them. In Arang, the issue is that Arang has less than a month to stay in the world and, oh, a monster wants her body. In Five Fingers, in addition to Ji Ho's family being psychos out to get him, the issue is that Dami and Ji Ho come from enemy families (long story). But the thing is, if these were fixed, there would be nothing preventing OTP bliss - if the Jade Emperor waved a magic wand in Arang, got rid of the demon and restored Arang to permanent humanity, or Ji Ho's family in FF took nice pill and the family history issue was gotten around somehow, the couples would be happy together. If the bad guys in Faith were taken out and ES decided to stay (and CY allowed himself to allow her to stay), there would be little warrior babies asap. It doesn't mean that the characters do not change or grow - they do immensely. But it's a different relationship dynamic than between Maru and Eun Gi in Nice Guy where all the obstacles are really in their own head, in their emotions and baggage (OK, so this is more true for Maru than EG). There aren't really that many external obstacles. But the internal ones are almost insurmountable.
I don't think one form of narrative is better than the other. I just find the difference fascinating.