The preliminary user research you refer is user interviews from which you created personas and empathy maps. If you are going to shoot down the value of upfront user research, then I think you also need to present your process for screening participants, the context used for conducting interviews (e.g. 1:1 or focus groups, location, contextual inquiry?), and the wording of the actual interview questions. Data from research is only as good as the methodology that is used to conduct that research. It is why divulging methodology is expected in standard academic research. I am unwilling to accept such harsh judgements like “Up-front user research is a form of product procrastination” or “busy work” or “overrated” without the evidence to back up such extraordinary claims. As the saying goes, “extraordinary claims require extraordinary evidence.” Where is it?