I don't get why some people say Mehmed doesn't have synergy. Org for horizontal expansion + Exp for vertical expansion means you can play for an expansion focused game (see my sig). Also, with Org + Exp, just add the GLH (cheap light house, cheap harbor). Plus, the synergy of having so many cheap buildings (lh, harbor, granary, courthouse, etc.). His UB fits awesome with Exp+
anyone? His UU is awesome if teamed up with cannons before your opponent hits gunpowder (e.g., Steel off Lib). Or, even just with trebs. One of my fav leaders for sure.
My best games though seem to be with KK. Incredible synergy. I can't think of a leader with a better axerush. Sensational really. 1st opponent with axes, 2nd+ with keshiks, mop up with cavalry that benefit from the Ger. Cheap libraries for specialists to keep up in tech. Cheap theatres/coliseums forto combat ww. A powerhouse for emperor and below imo.
His UU actually has negative synergy with the Exp trait in my estimation. Exp is useful for having large pops, drafting(whipping) Janus is best done with small cities. He'd be far better with cha or anything else good for the Janu. Bonus

Shaka, KK, and any of the English all have better synergy.