What we keep being told is that the product owner owns the
relationship to the customer and knows exactly what the customer
wants, and that the tech team is only supposed to have opinions on how
to accomplish the feature technically and not evaluating the merit of
the feature or modifying the feature in any way.
Well there you go. You've had your role on this project defined very clearly. Give thanks to whatever gods you believe in for such luck. Now, if the UX is crappy, there's no chance in hell that you will get blamed.
And honestly, this sentence makes a lot of sense on the surface. The Product Owner knows the customer best, as you would expect. Have you considered that beyond being weird about taking your suggestions, that they might actually be RIGHT with theirs?
I guess I just don't see why you are fighting this.
in the past, questioning the product owner has led to career disaster.
This sucks on the surface, but again, remember that the organization has very clearly defined the roles. Try the reverse: lets say that your org has said "The Devs pick the tech decisions. PERIOD." Now imagine if a Product Owner or UX guy starting coming around and asking you to switch from .NET to Ruby On Rails "cause its faster". You know you'll be integrating with SharePoint and Office and such, whereas he doesn't, but he REFUSES to accept that you know better without you providing test cases for why .NET is superior. I can bet you'd be writing this question a lot differently, it would prob be phrased "Why wont this UX guy back the f*ck off on MY domain???"