Just to add some more info on this :
Pet dragon exp is connected to relation of your and enemy army. SO if you start battle with X total leadership (example 1 paladin , 10 bowman, 3 inquisitors = 1020 total lds), and enemy have Y lds (10 black dragon = 25000 total lds). And if you use some pet skill that say you`ll get 10 exp final gain is 10*Y/X. Meaning more enemy units bring more exp. During battle you kill enemy and lose some units also, so total leadership ratio decreases bringing less exp each turn. And in the end you`ll probably get 0 exp, when enemy army is almost destroyed.
There is cap for this, but i`m not sure what value it is. So you cant start battle with 1 unit cast invisibility on it and kill whole enemy army with rage for 1 million exp. But for lvling pet dragon, you must take in consideration whole battlefield leadership ration enemy/you.
As for your question, first turn in battle mana ball gain is lets say 60, but each turn after you get less, and less. So it`s not 3000 for maybe 50 turn, but 60+50+40+30+20+10+...+1+0. So 800 exp per battle so soon is great gain.
In the end, i`m still on old patch 1.3. Maybe in latest patch is some change making you stop getting exp after certain number of turns. Like for medals, spells counted toward medals are just first 10 battle turns. Check exp on turn 9 , 10 and 11 in battle without killing any enemy units, to see if there is some difference.
Have fun
