I'd say there were a variety of reasons to choose civ switching over leader switching. Money and effort was certainly one. Research that said players invested more in leaders was another (I personally think they misinterpreted the research--at least here it seems more common for people to say they identify their opponents with leaders but themselves with the civ; that's certainly my position). Losing meaningful diplomacy is a third.I meant, they chose civ switching over leader switching because it is less work making new civs than making new leaders.
Considering Greek culture is foundational for Western culture, I think Greece into virtually any European civ makes perfect sense.having the Greeks switch into the Normans