Regarding dueling. Sometimes in duel players get to see opponents do weird stuff. Wonder why? Maybe they live in far away region from the server and there is latency.
The casting is currently client per server request and respond. Meaning you cast a spell and client needs to wait for the round trip from the server back to the client. Therefore the 10 second window of per turn may result in really a lot of waiting.
Next the player may not have enough time to observe and react to what the opponent is casting (looking at the current spell slot and heat). Example: 4 heat 4 slots; oohhh most likely it is cloud, lets reflect it.
By the time the information reached the client it is already too late as time is slipping. On top of that they have to deal with the latency to register their spells which makes matter worse.
This duel system is great for localized play or region segregated. I think the duel is going to be fun eventually if they resolve the regional latency and match making system.