I can’t do a touring plan that uses Park hopper options for both parks on the same plan - correct?
It actually seems mean to expect this when I can barely do basic multiplication considering the algorithms at work in the current system as it is - but just checking 
Correct. I always make 2 plans on the same day one for each park and create breaks for when I will be in the other park.
Ditto on this - works just fine to adjust the hours of your separate tours to match up with your park hopping plans. One thing to remember, leave enough time between parks. It almost always takes longer than you’d think.
I leave at least 15 min and also make sure walking time from the last destination in the first park plus the walking time to the first destination in the second park is accounted for on top of that and that’s plenty of time if you will go straight from point A to point B & even allow for a bathroom/hydration break. This also assumes it’s a usual day without backed up entry lines.
In reality, you may find that your family (like mine) will find something to distract them on the way in or out (we always seem to stop to look through shops around park hops) or that entry lines are backed up with a slight delay (more than 10-15 min. is very unusual though).
I have thought this exact same thing and I know it seems greedy to want this option BUT I want it all the same…one plan hopping parks. I might even be willing to pay more in the subscription for that service.