Your strategy to make DEC earning a top priority was a great decision.
It is most important to play limited, quality battles with lineups where you can win.
My priority list is:

1. Tournaments
2. DEC
3. Daily quests (only if the daily quest team is the best team to get me a win)
4. Top 10 or 25 ranking for end of season booster pack rewards (try to rank up 2-3 days before the season ends, but try to avoid the last 24 hours which I have not been able to avoid)