Yes, yes I did... And don't tell me you pay for them with gems, because it's a one time payment and like the gem mine, after a period of time the gain you got would have paid off the initial gem investmentAre you saying the Sparring Pit doesn't apply any XP bonuses because its free XP?
The answer is not correct and some cases make you think champs xp same as account xp, they are different.
You ONLY get account xp when you complete some certain campaign & dungeon stages.
You could have earned champs xp when possible.
Imagine you do dungeon with all max lvl champs, you only earn account xp but not champs xp.
Sparring pit give champ xp only.
The sparring pit is passive XP gain and XP boosts are labeled as "The amount of XP your Champions earn in Battle is increased by 100%".
Personally though I wouldn't want to have to log in twice as much to keep checking my sparring pit if I had an active boost. If I wanted to farm XP, I'd just farm XP.