During actual flight testing of engine out procedures, it was interesting to note just how difficult it is to make the climb and not violate the missed approach surface, especially if you are configured for landing, and near the 140kts CAT C speed....
5% at 140kts groundspeed is about 710ft/min. This might be a struggle in hot conditions high elevation and high weight.
2,5% is about 355ft/min at 140 kts.
Sorry but I really don't believe that most twins will struggle with 2,5% in reasonable conditions.
Offcourse as a performance engineer you will be presented with the difficult cases, probably the usual suspects. But on most airports I suggest that twins can easily handle 2,5% EO.
I haven't seen anything from our performance calculations LPC NG (A319/A320), that suggests otherwise.
And offcourse there are techniques to create a higher actual gradient: lower flap setting for landing (less drag in missed approach climb config) and a higher approach speed (more energy to start with)