more of a ... than... 是一个常用句式（语法上叫择比结构），意思是“与其说……不如说……”。

你的句子意思是：与其说他是位国王，不如说他是位诗人。

又如：

It’s more of a guess than an estimate. 与其说是估计，不如说是猜测。

He is more of a poet than a musician. 与其说他是个音乐家还不如说他是个诗人。

This book seems to be more of a dictionary than a grammar. 这本书看来与其说是本语法书不如说是本词典。

It was more of a meeting than a party. 与其说是一个聚会，不如说是一次会议。