Donaldson and Harrison were thrown in way too soon and had to learn on the run.
This is a bit of a tangent but these guys absolutely need to be playing Super Rugby in their early 20s if they are really aspiring to be stars. We (collectively) say that young players need to be held back and not exposed to high level rugby too soon but then lament that the guys we are playing against from the Northern Hemisphere have a huge amount more professional games of experience at a similar age.
It's absolutely true that these guys starting their career playing in a bad team have a tougher time of it but they also need to be playing.