Westjet are none too clear what the extra medical requires. However, it is very unlikely that they have dreamed up new tests to identify diseases missed on a 'standard' medical. The medical industry is investing literally millions into trying to develop such tests and they dont exist - PET scans for example may identify the risk of future cardiac disease but if we were to ground everyone with calcium deposits the industry would fold.
Far more likely is the scenario that they are setting tigher limits on known diseases such as hypertension. Many of the CURRENT limits are dubious in terms of scientific predictability and certainly err on the side of caution, so if we are totally objective the conslusion must be that there is no increased safety, no extra information for the pilot but merely more pilots being grounded or refused employment.
If any of you are worried about 'missed' pathology, go and see a doctor. Dont rely on a medical and dont support a system that denies people employment otherwise other employers may roll it out.