Missed Approach Climb gradient and missed approach requirements
We're mixing things here. 2.1% is a certification req as per EASA CS-25.
Operationally we should comply with EU-OPS and PANS OPS doc 8168 which prescribes 2.5% as procedure design gradient unless otherwise noted.
The requirement is always for One Engine Inoperative.
Note that from PANS OPS revision 4 onwards the level acceleration segment (6nm@800ft HAA I believe) has been deleted. This means now that 2.5% gradient must be assured OEI until MSA/go around altitude. I.e OEI acceleration must be delayed...
Some states such as France have, despite having constructed i.a.w. PANS OPS 4/5, catered for a level acceleration segment i.a.w. chart note. E.g. No level accel prior to xxxx ft.
Rgds