Going for three on stone early as Byzantines against Sengoku is very nice because Sengoku's age up is slow and delayed, allowing you to quickly reach Cistern Level 5 and boost your economy.

It feels horrible to play cavalry against Sengoku because their Yari are way faster than normal horsemen; it's better to play fully infantry until Castle Age.

Getting camel riders for the debuff against mounted samurai is highly recommended.

Against Sengoku, mass spearmen get destroyed by mass cavalry; they don't even need archers to counter them.

And it makes a lot of sense when you're up against Sengoku or any civilization really with unique horsemen. You don't necessarily want to fall behind when it comes to the strength of the horsemen in the engagements early on in Feudal Age because horsemen can be a core unit in these fights. The Yari cavalry getting +2 damage and the additional attack speed with the Daimyo as well getting an additional +4 damage on your own horsemen, plus the active healing during the Triumph can help Byzantines bridge the gap and actually take some stellar engagements there as well.