Why does the 16 climb so much better?
XVI is such a good climber because it uses a Merlin designed for low altitudes (i.e. MA alts) rather the Merlins for the F IX or Griffon fitted to the F XIV.
Get a XVI up to the alts an F IX or F XIV was designed for then you'll see a difference.
There were 3 series of Merlins -
Ones designed for low alts eg Merlin 66 fitted to LF's
Ones designed for regular use eg Merlin 61 fitted to F's
Ones designed for high alts eg Merlin 70 fitted to HF's