Product should, definitely, run user research along with Product Design. But what I find is that people in either have a problem imagining a solution that's a couple of orders of magnitude easier to build, but also much easier for our customers (usually boils down to making the right choices for customers — the savings are not in the common "choose good defaults", but in actually removing flexibility that's needed only in 1% of cases).

Thus, I insist on engineering being involved early to put real world constraints on wild ideation ("it would take 3 months for 5 engineers" quickly changes what's a must-have :)) — sometimes, a curious, critical mind can expose things like these without having to do the research or user testing themselves.

Now, throughout my 20 year career, it's been very rare to find a product person who will both understand customers deeply, tie their needs to business value, and be able to formalize the intersection of these in a form of good requirements for design and engineering to eventually build!

So I really believe an engineer's (and design) role there is to serve as a sanity check as they dive into actual building — does this really make sense? If they do not, they run the risk of a project completely failing or perhaps not even shipping once someone else questions the value of continuing to invest in this 3 month project 9 months in. ;-)