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No i cannot site any stats but i accept the ones that you have. I speak from my own experiences of travelling on the ECML and only bother reserving seats on weekends. The early morning "business" trains into Kings Cross don't seem as busy as pre-covid and the late afternoon/ early evening...
I am not sure that XC services delay LNER services between York and Edinburgh. XC services are timed for 55 minutes between York and Newcastle, with stops at Darlington and Durham.