The app gradient is based on OEI and usually the most limiting.
Approach climb OEI gear up, landing climb AEO gear down, and different speeds. As to what limit may be critical, that will depend on the aircraft. The big problem is going to be reconfiguration and acceleration to get to the appropriate speeds
The missed approach is based on a minimum of 2.5%
As a procedures design consideration but doesn't consider what the aircraft constraints may be
if you cannot make this, then you cannot perform the approach
or you need to adjust the approach by, for example, adopting a higher minimum
most cases at max landing weight this is not a problem.
The OP's concern was for a maximum takeoff weight situation with an immediate return .. things might be a lot tighter now, don't you think ?
To get extra performance being overweight, consider a bleeds/Packs off landing
For a significantly overweight landing, that is a bit like rearranging the deck chairs on the Titanic, methinks.