this is of HIGH relevance to the all engines operating takeoff.
You are mixing two concerns. First, the takeoff bit and then the subsequent departure. Both need to be considered and the more critical determines the final departure weight.
unable to met the 15.2% climb requirement for all engines operating.
Again, not relevant to the actual takeoff calculations but may become the critical path for final weight figures. The two must be treated separately and then the more restrictive becomes the critical figure. Not philosophically different to the case where, say, the enroute cruise OEI weight limit to clear the mountain range restricts departure weight below the RTOW.