This started as a great feature, so I am not sure why SP decided to kill it right away.
Currently people are not playing. It takes 2-3 minutes to find an opponent. Classic duels were great as low threshhold playing. Now the option seems to be sinking in 20 gems for a low chance of getting rewards that are slightly similar to those 20 gems.
My rewards from finishing the Grand Duel today: a time limited avatar I don't care about and which is from an OP stupid monster anyway; 2 grand duel tickets (seriously, need to win another one to get one for free? :/); 25 elemental cells from an element I do not really need; and 12 elite monster stones which probably will have some kind of use in the very long run.
Hardly worth the 20 gems.
On average people will win 2/3 battles, not 9. Rewards for 3 battles won are a joke compared to 20 gems.
Only reason I will continue playing them is because it's the only feature of the game I currently enjoy, If I still would spend gems on wars and races and ranking up monsters, I would consider it a very bad investment.
Former co-lead of Resurrection of AMAB and Untamable; Retired: Parked in the Fifth Element; Make War, not Races