Holly's potential as a good ship for Hyz for me is that if they had interacted more in Efrafa and formed a bond whilst Holly was there, then I could see it potentially being a good tragic ship. But Holly's stay in Efrafa is so brief and their interactions so sparse and factual that it fails to have the impact that I think they were going for.
I honestly find writing any romance hard^^ But I think that it is harder to write a convincing romance between two characters who meet for the first time during your narrative because then they obviously start from scratch. Going for love at first sight is often the easy route then but whilst I believe it does exist (my parents tell me it was the case for them too), it is hard to sell, especially these days.
You instantly fabricate a connection where before there was none when without love at first sight it would take time and devolpment for there to even be the beginnings of one.
On the other hand, if you write a romance between characters who knew each other before your narrative starts then you have the advantage that there is that connection from the get-go and you don't need to show it being formed. Childhood friends, for example, are very convenient for a writer and make it much easier to get away with showing limited scenes showing a forming bond. If they had established for example that Hyz had known Holly before and that they were friends then their meeting would take on a whole new dimension and even if they kept largely the same scenes, it becomes easier to get away with saying they loved each other without it seeming too sudden. It wouldn't be perfect or even necessarily great of course just easier.
Hammy, Holly's idea to make Hyzenthlay smile was in the end to just tell her how beautiful she is.