man if you want 30/30 heroes you should be able to farm de without them.
I recommend you to upgrade both if you can. when you reach the point you cannot upgrade both always upgrade bk non stop and use queen for raiding. this way your queen can help you more than BK.
In the first month of th9 I farm de with:
1- both heroes non stop upgrading
2- lvl5 gibarch and barch
3- both drills non stop upgrading to lvl6
4- use gibarch in crystal 3 non boost
5- playing 3 hours per day in average
I could farm enough de to upgrade both heroes non stop to lvl15 + dark troop in LAB.
After lvl15 it is harder so I occasionally have AQ for farming (BK was in non stop upgrade to lvl30)





