What decides if additional GA thrust required

[rudderrudderrat]

I defacto,

Would that be true for higher than standard missed approach climb gradient?ie 2.5% and above?

Before commencing the approach, we have to calculate our engine out missed approach climb gradient using the current weather conditions, and adjust our DA accordingly (like Zurich) or refuse the Approach (like Naples Rwy 06 ILS Z). I'd be very surprised if you don't have to do that.