FE Hoppy, we're getting there slowly. They key point to the big picture of this admittedly confusing matter is fact that there's two sets of rules:
One is aircraft certification and another one operational is EU OPS or FAR. They're unfortunately not harmonized as you seem to assume
OPS 1.510 covers the missed approach requirements including the need to satisfy the published climb gradient when above 2.5% or a minimum of 2.5% when the DH is below 200'. But, in both cases the procedures assume the GA begins at or above the published minima.
and the rule doesn't say anywhere you're safe no matter what the MACG might be, on contrary it says;
For instrument approaches with a missed approach gradient greater than 2.5%, the expected landing mass of the aeroplane shall allow a missed approach with a climb gradient equal to or greater than the applicable missed approach gradient in the one- engine inoperative missed approach configuration and speed.
The use of an alternative method must be approved by the Authority (*)
Thus in our case for the approach to ILS 16 CAT I in LSZH you have 3 options:
1. Fly higher minimum published for MACG of 2,5%
2. Fly CAT I minima and reduce LW to meet 5% MACG SE
3. Fly CAT I minima and retain MLW but follow EOSID in case of SEGA.
As we saw earlier the operator may do generic calculations so as far as I see my performance layout for RWY 16 says A 320 can follow published MA with MLW CONFIG FULL only when OAT is below 0 C otherwise EOSID.
It's pointless to discuss the case of a GA below DA IMHO.
as it's self-explanatory Cheers