Very!
There are about 8tph running between Leeds and Micklefield – 4 TPX, 1 XC and 3 Northern.
This limits the number of trains that can stop at Cross Gates, Garforth, East Garforth and Micklefield, because it delays all the fast trains, and has a horrendous impact on reliability because any train running late will cause knock-on delays for other trains.
Years ago, I used to commute from Church Fenton to York, and there would be a collective groan across the platform if ever a TPX or XC train came through within a couple of minutes of when our train was due, because we knew that we then had the best part of 15 minutes to wait before the stopping train would get to us, even if it had left Leeds hot on the heels of the fast train.