I'm looking at this from many different angles. If I stay at Universal for 15 days, I'm staying at Aventura or CBBR since I can't justify the cost of staying at Royal Pacific. If I stay at Disney for a week, I get all the benefits like FP, Magic Bands, charging to my room etc plus I won't be paying for parking (I'm from the UK) which saves me $22 a trip to Disney or more if I need to get an Uber if I want to drink in Epcot, plus the $12 a day parking at a Universal hotel (I know that the more expensive hotels charge more). Staying at Pop Century is the same price as CBBR or Aventura so I'm saving money on parking plus I don't need to drive because of Magical Express and a good transport system within WDW and I can pick a car up at Disney on my last day no problem and drive to Universal.
Overall, staying at Disney will save me about $400 which I can then put towards staying at Royal Pacific. Granted I'll have fewer days on site at Universal but I'll probably still visit the parks the same amount of time and I'll save a huge amount of time by having Express Pass and get the benefit of staying in a much nicer room, closer to the parks and major benefit of being able to skip the queues for restaurants at CityWalk.
I had planned on getting free Disney Dining but from what I can see, all the deals are more expensive than buying it separately plus I feel like I'd be dining to justify the cost.
It doesn't get said very often now but it's actually cheaper to do things the Disney way.