In theory learning the foibles of flying a swept wing prior to the Type Rating Course should mean you have more capacity to learn the specifics of the aircraft, less repetition of exercises and so less chance of extra training being required.
Even if you are paying for the course airlines can and do pull the plug if much extra training is required, starting the course doesn't guarantee getting the type on your licence.
In practice I have seen candidates with no JOC get through and conversely some who have completed a JOC fall by the wayside.