So, let's get real BaronG. Here are your choices, you have a company FO with the required licence/type/hours and suitability. To get him on line as a captain will take a few SIM sessions and checks and some line training and checks. He has considerable route and platform experience.
Alternatively you have a direct entry candidate who has the required licence/type/hours and perceived, but as yet untested, suitability who will require a few SIM sessions and checks and some line training and checks.
If a company sees the need to take in DEC it is likely to be a case of either just not enough SIM time available for a LHS to RHS conversion to meet contractual requirements of qualified pilots on site, a very short term situation, a more or less one-off thing, or they simply don't have the necessary number of licenced/type/hours and suitability qualified FOs for upgrade. It is cheaper to promote from within than to employ DEC if you have the required material to start with.