"I would compare CWL-GLA to LDY-GLA which Ryanair are now doing 6x weekly."
Different markets. Strong ties between the NW of Ireland / Northern Ireland and the West of Scotland so a lot of 'family' traffic on LDY - GLA along with a degree of 'sports' travel. In my experience on flying GLA - CWL its mainly suits during the week and never ever enough to even part fill a 73-8. The only time an aircraft of this size is needed is for Wales v Scotland at rugby or football.