I would also benefit from keeping both as I’d like to use my monzo CA as my actual CA rather than in the same way as my PP.
Have you checked out the Pots thread? This is something monzo seem to be working towards (it’s on their road map for within the next 3-6 months) and I imagine this feature will negate the need for a PP Card by allowing you to keep whatever you would normally keep in your CA in one pot and having whatever you would have on your PP in your main pot.
Check it out if you haven’t seen it 