Yes I'd predict train and bus will be lucky to achieve a 1 per cent market share of LBA travellers. At that type of airport the vast majority are going to use car or taxi anyway and another public transport option doesn't figure. It might do better with employees at and around the airport. There will be a small market to/from Leeds city centre for whom train can avoid the congestion and unreliability of the A65 and A660. As said above it's a parkway station with a bus to the airport and will stand or fall on that basis.
In my view there is a big difference between the arrangements at Luton and Stansted in perception terms. Two lots of waiting time at Luton, bags to lug. Not that great really.