Man, figuring this out gave me a headache at first. 'Drakos' is definitely part of the 'Uncharted Stars' saga, which is like a mega-series. It's a standalone adventure, but the characters and political fallout directly connect to the events in 'The Serpent's Wake' and set up the climax in 'Worlds Unmade'.
Here's the rub: publication order is fine, but the author wrote a later prequel, 'Cinder of Empires'. I'd say skip that until after you finish the main trilogy. Start with 'The Serpent's Wake', then 'Drakos', then 'Worlds Unmade'. Reading 'Drakos' first would spoil some major reveals about the protagonist's lineage. The prequel hits harder with the context of what his family becomes.
The anthology 'Tales from the Drift' has a few side stories set between 'Serpent's Wake' and 'Drakos' that add flavor, but aren't mandatory. I accidentally read 'Drakos' first and spent the whole time confused about why everyone hated the main guy's uncle.