you should limit exp of dragons and heroes to lev 25.
not for say but i got between my army of charriot (as deposit) and town 260k gold.
i istantly bringed 2 new hero to lev 40. (in 1 min)
where my original hero trained manually to lev 41 toke me a month and my city is able to pump money at rate of what 100k day? maybe more if i convert all workers to gold or sell stone/wood/foold for gold daily also