Does DEF really reduce NOx emissions by 70-90%? – GWC Mag

Is there a discussion about the usefulness of DEF or is it pretty much a clear cut wonder-weapon against emissions?
I read somewhere that NOX can disappear within seconds spontaneously and its not clear if DEF is that much effective because other things have reduced emissions so much already.

This source claims it reduced NOX by up to 90%.

This graphic implies that actual emissions in the real world aren’t that much better (dark grey cloud):

https://vcoe.at/service/fragen-und-antworten/was-sind-stickoxide-und-wie-schaedlich-sind-sie