The largely unreported number of attacks by Afghan soldiers on their own forces bears this out.
Not really surprising. We in the West keep thinking these people are "Afghans" in the same way that we consider ourselves to be "Americans" or whatever nationality. We assume their national loyalty is roughly the same as ours. In Afghanistan, national identity is usually a second or third tier concern. To expect them to gel into a cohesive force and put aside their other identities and loyalties in favor of a national identity is foolish whether we are talking about building an army or limiting corruption.

Look at what's happening to the Syrian military which is fracturing along ethnic and sectarian lines even though it was a cohesive national force for several decades. Yet we expect to actually build a national force from scratch in Afghanistan? It might work long enough for us to exit Afghanistan, if we're lucky.