Thus all our F/Os appear to be gaining their ATPLs on an official, CAA sponsored dodge that would be illegal in the rest of Europe as I understand it. Strange!
I agree with all your comments about earning the signature, and briefing the roles in advance, however I'm not sure that PICUS can be considered a "CAA sponsored dodge".
Here's the EASA Part FCL definition:
PICUS flight time: provided that the method of supervision is acceptable to the competent authority, a co-pilot may log as PIC flight time flown as PICUS when all the duties and functions of PIC on that flight were carried out in such a way that the intervention of the PIC in the interest of safety was not required.