To add a bit to mutt's comments, FAR 25 deals only with certification while Tprocedures drawn using TERPS, PANS-OPS or any national standards differing from them (unusual, granted) are designed to achieve the lowest reasonable minimums and compatibility with the ATC structure. Many procedures, especially SIDs are drawn, not to optimize payloads or to minimize climb gradients, they are drawn to meet ATC needs. The procedure designer cannot anticipate the performance characteristics of each plane using the procedure, he assumes AEO operations. It is up to the operator to plan for the engine failure case, not the designer. Meeting FAR 25 OEI climb gradients is irrelevant to DP or MAP and to achieving optimum gross weights may not happen by using the published procedure and using the published procedure may not (likely not, in many cases) provide the greatest margins in the event of OEI.
It is, in many cases, erroneous to plan meeting the specified climb gradients means the operation is being done in the safest manner. Many think planning to fly the SID or MAP using OEI performance data is best, many would be wrong.