I like this manga. But to be honest, the main point that Ryuzaky is a protagonist don't make any sense. I mean, he have all traits of a antagonist, not a protagonist. He is a egocentric prick afterall
My impression is he's probably the stereotype of protagonist from older era, or from story for younger age segment.
The highschool romcom protagonists we're familiar these days are usually like Kotaro, teenage boys who are unsure what their own strength is, no idea what they want to be, and afraid of failing in social relationship. Unlike characters from older stories, they don't quickly turn their fate around in the early story and become hero, but go on a long and frustratingly slow growth.
Ryuuzaki might look like an arsehole from our point of view. But from perspective of a story with him as the protagonist, he is like shonen battle MC who are completely confident about their sense of justice. He do talk no jutsu about what he think is right, overwhelm his opponent with that confidence even though what he said is actually cliche or shallow.
Also remember that he is dense as an MC could be, so he never thought the other girls loves him (or Shiho hating him). He doesn't destroy people with intention, it just happen as consequence of his personality.