Shipping running code is obviously always a top priority. Non shipping is bad, not running is bad/worse.
This is the kinda thinking that crashed two space shuttles. There are worse things than not shipping, even if it means the project gets scrubbed. Sometimes safety or durability has a higher priority than shipping. An older less efficient system that works is more valuable than a new one that is unreliable. A new capability isn't worth it if it gets you killed.
and loose conventions No idea what that is supposed to mean.
What I mean is that the following is from agile's founding document:
Individuals and interactions over processes and tools
Working software over comprehensive documentation
Customer collaboration over contract negotiation
Responding to change over following a plan
Try telling the FDA you value "Individuals and interactions" over following a defined CGMP or "working software over documentation" and see how far it gets you.
rigorous requirements requirements in agile projects underly the same rigor than non agile projects - otherwise they are not "requirements".
If your design and implementation is subject to a very heavy, long, and expensive V&V process, you can not "spiral" on them. You can't freeze a design if your requirements are subject to customer change at the end of every 2 week sprint.