Leeds is what 90% bucket n spade or hen/shag parties ?? few solo travelers, so any transport method that becomes more expensive as more people in a group use it will naturally revert to a car or a cab.
The park way is a sham, few use it at EMA I think even the free bus shuttle that launched it have stopped now ( stand to be corrected) what you will end up with is a park n ride for the people of north Leeds to travel into Leeds, on top of which the buses like 757 will stop and they'll just take you to the park n ride, they run at a loss on subsidies, LBA will then be able to tick the ' green box' the last thing LBA want is you to turn up on public transport, far better (for them) to take your car park money, if they lost that they would have to increase fee's to Ryanair & Jet2 guess what Ryanair would do?
It would be like a turkey voting for early Xmas, this parkway nonsense is perfect for Bridgeport, they are not stupid ( unlike the clowns in Leeds city council) they know few will use it even if it went into or under the airport and no one will fund it.
Leeds have been predicting 5m a year for over a decade, Leeds Approach is not wrong when he says it's in the wrong place, but it won't move, it's too big to move too small to reach out beyond its Holiday routes and too close to Manchester to grow long haul and that's without even thinking about its runway/weather limitations.
So stick with what you've got, it's a good little airport for its target market