The nature of feedback means that sometimes you get an A* with no amends or it gets ripped to shreds. Some of it valid, some of it nonsense. It's important not to always be compliant.
Sending your precious copy to a client/stakeholder is nerve-wracking enough, it's your masterpiece, there's not way they won't like it and hold it up in their Town Hall updates to marvel at its magnificence. But what if they hate it and you completely misunderstood the brief.
Of course, being a copywriter means you've honed your diplomacy skills. You need to understand and question the brief in a tactful way, now you need to defend your work in a tactful way.
We're constantly navigating client privilege.
They're always in charge. They set the budget, the direction and the schedule. You must comply.
However, it's important to remember, they hired you for a reason.
To write awesome copy that makes their brand sing and their products sell.
So when you get feedback on copy that you disagree with, say so and say why. Use the knowledge you have from testing and experience from other projects.
Even if the challenge is they want copy where you don't think it's necessary, so you're writing for the sake of filling up a space, so you're not saying anything. Wasting a reader's time is sometimes more damaging, as they turn off.
Firstly, it's the brief. My mantra when reviewing briefs to give to the team is, "shit in, shit out", so challenge that if it isn't clear what it is or what they want you to do.
I once had a meeting with a product manager to get him to explain the product to me like he would a child. From that, the brief (and copy) basically wrote itself.
You need to pick your battles. I outline when I send it off for review that they are checking for sense and accuracy. This seems to ward people off from commenting about the tone and grammar (I'm sick of people telling me I can't start a sentence with the word 'and').
The battles I tend to fight, increasingly, is asking existential questions about copy on the page. Interrogating what each element is on the page, why it's there and what does it do.
On a copywriting level, it's about leading with the benefit and getting rid of superfluous copy that the marketing manager thought was amazing, but didn't actually say anything (typical) and show, don't tell. The biggest fight is about writing things in plain English and especially, writing things colloquially.
It's easy to back down and comply with the people who pay your bills, but it's more than your professional integrity is worth. If it's a big, high-profile project, think if what's been produce is something you'd put in your portfolio.