For those 30 points, what about upgrading the Shredders to Blasters, then keeping the Dissies on the vehicles?
TBH, I have totally neglected shredders for two editions now. Blasters have just been so nice, especially when you sprinkle them throughout the army to the point of saturation.
Also for the DL/Dissy debate, I guess it comes down to your meta. I have a lot of ++ saves in my area, so those couple DL shots generally bounce off. But a few Dissy shots generally get through and chip away at the target. I would recommend not mixing, and fully leaning into either DL or Dissies and seeing how it goes. Would give you a better handle on which to take in the future. I do recall back in 7th someone going fully into DL Raiders (not taking any RWJF or Ravagers, just Raiders), and doing really well, against all expectations.