Unlike several other airlines, CX hires S/O's with a minimum of only 1000 hours single engine piston. DEFO's require 1000 hours of jet transport or command in a turbo-prop/corporate jet. On the street, the difference in years to acquire the DEFO minimum qualification from an S/O's minimum qualification point would be several years. I suspect an average of 3-5 years unless you're very fortunate.
My point is that S/O's should have their seniority frozen for 3 years and then upgrade at that point.
CX used to hire DEFO and I think they should now offer the new DEFO position to any S/O's that meet the minimum qualification of DEFO prior to their joining point at CX. Those that do not meet the minimum should be given an upgrade at the 3 year point in priority over any new-hire DEFO.
That's my 2 cents.