I am not really sure the Theory isn't completed yet but i hope this helps you a lot well i have been to Darsil many times even my DE is lvl 31 lols but from what i see yes it is good enough to be publicist. lol My dear friend PatawaXD here asked me to make it public lol .
well the statements are :
1 - Not destroying Hub grants a higher droprates .
2 - Killing Lupi/Rupi/Gupi dosent recude drop rates but it give u buff of max hp when killed.
3 - Killing Rapid dosent reduce drop rates but instead give 100% enchanment gem drop at teamed Dungeon
All this applies to Darsil and Bitter core , other dungeon well i ahve try i dont try other dungeon that much.
statment (1) proven wrong when we received more enchanment gem than usualy , that we suspected.
Statment (2) we accidentally killed lupi but we get 3 rare drop at ogung well can say lucky since we didnt get much earlier b4 this.
Statment (3) everyone kills Rapid no ? lols for the gem . well killing it or not killing it is just a waste of them just kill it it dosent reduce anything.
This might change as game system usualy changes drop rate % so yea not 100% reliable but a good information to keep in mind of.