The optimal strategy will unfortunately be to skip days where you don't have a good deck for the given focus and let the ECR recharge until a more favorable context. You'll want to play more when you have a bigger edge, not wasting ECR on lower return context.
But that raise a good question : Across a whole season, what will be the breakdown of the ROI contribution for each of the earning aspects : Daily focus, Season Chest, Battle rewards DEC (SPS soon!). In the past, it always have been more profitable to play for the win over the daily quest. Completing daily quest were incidentals.. and they still might be with the new format.