That’s not how software is done though.
Product managers are in a constant negotiation with engineers to decide what to do. There is a lot of back and forth and exchanges to arrive to a set of stuff that can then be built.
That’s what the agile routine is about.
As a team, we can't just go all vigilante, but we can push back and have at times gone over other people's heads to make sure the proper people understood the problem. Most of the time we got what we thought was best for the customer by going over people's heads, but there's been plenty of times that a middle ground was reached.
The main thing is to not just say "we can't". Our job is to deliver solutions, not products. If there is a problem with priorities, we find an acceptable way to make things "work". Maybe that's adjusting timelines, or features, or just asking the customer how important that timeline is to them. I can't tell you how many times I've been told about "deadlines" that the customer never actually said was a deadline.
Us: Yo cust, can we slide that project 2-4 weeks?
Them: Sure. Heck, move it back 2 months if you want, but we absolutely need to start testing on our end in 3 months.