I'm not sure if this would work.. but would scoring systems be changed to have a third group for DPP players? Bat only players have something that supports them, bowlers only the same, and then all rounders/DPP have a more balanced system (that maybe mirrors the bowler and bat systems but slightly less points per action? Seems like some of the issues come from there being a class of players that effectively get to double dip across the two scoring systems, meaning anything that tries to balance either will also continue to benefit all rounders.
This is one of the suggestions I mentioned earlier, along similar lines. Unfortunately, its probably too complex to bring in, but I agree, a bit part of the problem is the allrounders getting multiple goes.
2. This one may be a lot of work but separate scoring systems for SR and ER depending on status. For example, if a player is bowler only and only bowls 1 over, I think they should still get their ER bonus. Similarly, if they are BAT only, they can get a strike rate bonus regardless of whether they get to 20 or not. This adds value to BAT and BWL only players, otherwise we still go after BAT/BWL or WK/BAT players as they provide more flexibility in our teams.