Its not exactly two different models being followed in development exactly, like your post seems to suggest.Whatever the model they have adopted, they have displayed a blistering pace of development in this filed.
PDR has to be done beforehand, is not cast in stone. It is just a part of processes that have been designed by us.
I still see Turkish aircraft taking to skies in a much shorter timeframe than we can.
Preliminary design and Critical design are not exactly same, now am not a aviation expert or defense expert to comment on how efficient it is to build a prototype on conceptual design. However I am sure there is a hell lot of difference, between concept and real life situation.
Still like you said the bird will fly first