Bloggs
It needs to be highlighted that the aircraft concerned appear to have collided in a controlled airspace environment. See and avoid was not the primary (or intended) separation method. This accident may highlight the inadequacy of see and avoid and your point is well taken.
Ulm
Nothing in NAS states that ADSB will be - or needs to be - in place as a mitigator prior to implementation. NAS is going ahead with or without ADSB. See and avoid may be the only defence in some circumstances. NAS acknowledges that new technologies such as ADSB may be implemented and supports them when this happens.
The mythical nation of 'North America', which NAS is based upon, probably does not have ADSB either!