They seem to be sharing them around as the X66 had 4 Darts yesterday at one point...Seems to be full Pulsar on the X66 today.
It will probably continue like that until the Scanias return.
It's probably better if Pulsars do the X66 but why should the 1/5/5A suffer, also people have been warned about no wheelchair access on the X66 but there is no warning for the appearances on the 1/5/5A, 2 and 8/8A over the last few day and parts of the 5/5A, 8/8A only have one bus an hour which is much good if you are in a wheelchair.