The EXP gained from Ranked Duel matches was at a level very much corresponding with the activity itself. (Ranked) Duel is a very important mode for learning a character by providing chance encounters of different matchups. Subjectively, it is also one of the most fun modes, albeit it can be rather frustrating when using a sub-S-tier character against someone abusing mechanics. The increased EXP rewards remedied the mode never having even been close to compensate participation.
In short: It was very good. Keep it that way.

PS: The Devs should play Ranked Duel regularely, especially with older or bad characters. It shows exactly where problems lie with the game. Really not hard to overlook the presenting flaws and find subsequent solutions.