You haven't misunderstood anything
iaf_22, that's exactly the way it is. Stinks doesn't it
You have 3 basic options available -
(1) For a OEI missed approach, use a higher minima, so that the lesser gradient lies above the obstacle-clear plane derived from PANS-OPS, OR
(2) Develop "Special" missed approach procedures for OEI operations, much as we do for the Takeoff case, OR
(3) Limit your landing weight to that at which the missed approach gradient, which may be higher than 2.5% (e.g. 7.0% for Hong Kong 07L), is achievable by the aircraft with OEI.
The first 2 are difficult to calculate, and option (2) is fraught with problems if you use the OEI Takeoff procedure for the same runway (but better than nothing although risky).
The best option is No. (3), which is what I provide data for in the Ops Manuals which I produce, safe, simple, and practical.
Regards,
Old Smokey