Given that there is no set syllabus for JOC (unlike MCC), and the content varies hugely between providers, it is quite surprising how many airlines are now stating that they will only consider candidates who have completed a JOC.
It seems that JOC is becoming a must-have for your CV, even if the particular airline you're applying to doesn't make it a requirement.
As there is a lot of autopilot use during MCC, whereas the JOC will more likely focus on hand flying and jet handling, it is possible that airlines realise that students with a JOC qualification will have an easier path through a type rating course.