Siphonator, defense oriented & Ram utilizer flamethrower footman, a Fire Ship on land, for the Byzantines:
It’s better for the Byzantines to have an additional unit from Castle like this, or like the Varangian… than a cosmetic reskin to their Fire Ship which other than that will be a useless change… or than a unique spearman.
Byzantine “Castle drop” play (which currently is average due to Cataphract is highly situational in that age) will be skyrocketed with that additional defensive/counter choice, available to fill strategic gaps related to opponent’s attacking army composition; next to Cataphract.