I'm new to the Descendants fandom, so I don't know if it's been said before, but I feel like the romantic love was less important to the first movie's conclusion than other kinds of love.
Sure, the whole thing of "I don't know what love is," seems, in context, to be romantic love, but:
Jay's arc is about learning to admit he cares for his friends and to trust them. On the Isle, he looked after them, but I have no doubt that he would left if it benefitted him. Evidence: the way he trampled Carlos during Tourney practice. His own dad taught that to him ("There's no team in I!") and I feel like that's something he learned the hard way. I don't imagine Jafar was a caring and soft parent. His arc is about learning to trust others- particularly, his friends. Romance was no part of it, no matter how much he tried to flirt.
(Edit: Jay treats them like Family. He just has to re-learn what it means to be family.)
Evie's arc is about self-love. The idea that she doesn't need a prince- frankly, she doesn't need anyone. Doug was nice, but I felt like he wasn't necessarily plot important. I understand her arc was supposed to be that she didn't need to love a prince, but it wasn't that she could love anyone, it was that she could love herself. The big moment where she's reflecting the night before the coronation, she's alone, proud of her grade- a B+. Not an A+, but she was proud of it. Her mom belittled her constantly, making comments on how even laughing could cause wrinkles. Evie's arc at its most simple is that she didn't need to fit this perfect standard to be proud and love herself.
Carlos' arc was similarly about self-love, but particularly about feeling worthy of love from others. He's used to being used and belittled by his mother, being told his worth is what he can do for her (ex. The comment about keeping him so he could touch up her roots and treat her bunions). He bonds with Dude, who loves him for no reason. Ben is nice to him, and you can see the wide-eyed surprise in his face. It's Ben's reassurance at the end that he's safe that's important to his arc.
Mal's arc is about True Love. And no, I don't mean romance. It was about her realizing her mom didn't really care for her, but her friends did. Lonnie's comment in the kitchens hit her especially hard- the others seemed to know that their parents didn't love them, but Mal only then began to realize that her mom did not treat her with love. I feel like this is what prompts the "I don't know what love is" comment to Ben. But she learns that the love she has for her friends- reassuring Jay (in and Isle way), protesting Evie doing Chad's homework, being Carlos' sheild when he gets scared, Jay looking to her and Evie when he's proud of his win, Evie getting her ready for her date with patience and kindess (despite knowing it was fake), Carlos sitting in their room to do homework just to be near them- that's love. And sure, she's starting to feel romantic love for Ben, but it's the love between her and her friends that saves the day.