Cutlery, I find that the best approach to P&D for me - is to just give myself 1 or two goals. Regardless of how boring those goals are, just grinding the maps to be most efficient. On days you don't feel like playing much, the Hunt! dungeons are really great for spending <30 minutes of time playing the game but netting 3-500k total XP for your minions (luck factors) - and the 500k number is really only something that happens with red/green/blue where you can feed the tiny dragons into the pendras. But - point being to just take it patiently, the other big thing to remember - and hades that you have is a big example. Even if you had 5x5* rippers and StE all done etc etc. Your team cost won't be enough to field them all at once anyways, so you need levels.
On days I feel like playing more, I prioritize ways to level up in the middle of grinding say a technical or for a drop, but always doing what I can to ensure I level when I want to keep playing. On days I just want to do something else besides 2 hours of P&D I just dump stamina into the Hunt! dailies. The more patience you have when nothing interesting is happening in your box (just need feeders to get them to evolve) I think the more you'll enjoy. Especially if you take on Technicals/Dragonplants/Hunt! The daunting xp curve that starts to happen from 50-70 for the 4* curve becomes really quite tame. I had the same feeling around castle of satan and thought that I would never get my box evolved.
The blue water dragon is on for another week, if you can beat the Adept version. I would highly recommend you put everything on hold and farm for marine goblins for your siren to take her orb conversion from 11 to 5. It gives you one goal, its decent xp, and you get some carbuncle feeders to feed as well. Keep in mind the marine goblin feeding is less expensive right after you evolve to level 1 again - so ideally if you could get that Siren to StE it'd be cheaper money wise but I'd recommend not missing out on the adept marine goblins. My rate of stamina/goblin was better than sea cave mercury. I'd average 2-3 goblins/15 sta and the exp was a tad better + you get a 4 set of lil'blues to save up for an all blue ripper team to destroy later red special dungeons.