1. In FAA region, 2.5nm is the min possible separation all the way down to the threshold. (we understand that)
2. In FAA region, 2.5nm is also the min wake turbulence separation for certain acft pairs.
3. In FAA region, (and not just there) MRS is not the same as WTS, and you will have to accept this. The numbers (nm) can be "equal" in certain situations, but it is just not the same... MRS "depends" on the aerodrome, while WTS is always there, prescribed, in force... (as a Controller, you apply MRS or WTS, whichever is higher)
4. The FAA region is not the only region on the Earth... So you will have to accept that in the UK the 2.5nm is not the only possible min separation down to the threshold. Guys here tried to explain the 4DME principle... But you started with occurrence reports...
I will again add an old document: see the difference
SEPARATION STANDARDS AT MAJOR EUROPEAN AIRPORTS
5. Your (FedEx) picture about 777 leader and follower... This is a B-B (category) situation. Never below 3nm.
But when a FedEx MD11 will be in front of the FedEx 777, the separation could be 2.5nm (Virtual Memphis with waiver ) or 3nm (presently Memphis - your words about no waiver). Do you think that wake vortices change with the waiver?
Finally, I do not understand where you want to drive the debate? If you want to show us all that the min separation standards are not OK, well in this case I think this is just not the right place... You can easily write a good letter to the appropriate authorities and explain your doubts. You can also attach all the statistics you posted here.
However, if you went through all the links, your eye should saw a statement (from FAA, EUROCONTROL) that; "Current ICAO, US and European separation standards are different, but all are safe. In the US or Europe there has never been an accident caused by wake vortex under IFR separations and procedures." Not my words... Today's link has also some reports.
I hope it will help.