There is a certain (but very historical) lack of significant late-game units for the byzantines, allthough the swiss-pikes bug gives them the opportunity to field those in the Late era.

Allthough I'd suggest that proper use of upgraded byz cav, pronoiai allagion and byz inf. negates most other "advanced" units.

You just have to adopt a really unique style of playing. and the same goes with the Turks.