Yona is literally just a fem shounen protagonist copy and pasted into a harem with guys. If all you want from this series is the novelty of seeing the shoe on the other foot, go ahead, but it just seems so bland.
...you do know that there is a type of anime called shoujo, right? Though for some reason Yona is not considered a shoujo anime (and I am curious if anyone really knows why; is it because she isn't a modern schoolgirl?), the idea of a girl surrounded by handsome, heroic men who protect her has been popular since the birth of anime (i.e. a practically identical show that comes to mind immediately is the classic shoujo series Fushigi Yuugi. There is also Pretear, Vision of Escaflowne, Fruits Basket and countless other titles of similar structure.
Shoujo anime is neither as violent or vulgar as shounen anime, because it usually is targeted towards girls (not that all girls like that style of anime, but it definitely has its target audience.) This might be what makes it vanilla to you. In regards to the romance, I can't really understand what you feel is forced about it when you think of contemporaries like Tokyo Ghoul or Nisekoi which trounce baselessly all over the idea of romance.
Nonetheless I can easily say it's not for everyone. I think having finished it you can at least appreciate the rather detailed world and the conflict of rule and government. Ironically the title shares many aspects with Korean period dramas - which needless to say is also ironic because all of the characters names seem to be romanized as if they were actual Korean names.