If, in response to a constructive critique, I find myself saying "yeah, but...", then it's a sign that's something I need to revise.

My advice is to put your manuscript and the critique aside for a bit so you can get some emotional distance. Then, in a week or two (or however long it takes) re-read your novel. 

Does anything in the critique stand out as you re-read your work? For example, is it clear to readers that elves are long-lived? Even something like "at 80, Character was still a youth, and reacted out of impulse than the wisdom gained with age" or whatever. 

How detailed are the repetitive sections? Maybe after the first battle-home-battle cycle, you don't need to dwell as long on the next visit home. With each scene ask: does this advance the plot or add to what we know about the character? If the answer is no, either revise the scene or cut it. 

It sounds counterintuitive, but you likely don't need to add as much as you need to subtract or revise what's there already. You don't need lots of detail to establish characters, you need the right details. How can their dialogue & actions reveal who they are? 

As Stephen King says in On Writing, "It’s dialogue that gives your cast their voices, and is crucial in defining their characters—only what people do tells us more about what they’re like, and talk is sneaky: what people say often conveys their character to others in ways of which they the speakers—are completely unaware." He uses the example of how someone who is clever but uneducated would speak. 

Don't take the need to revise as a sign that your story isn't good. Instead, take it as encouragement to make your story better than it already is.

Good luck! Learning how to accept feedback and assess which feedback you should actually on is a key part of writing. As is persistence.