I've had plenty of experience in dealing with people who don't respond to criticism well. I was one of those people myself.
Mostly, the people who had a hard time responding to constructive feedback were young. They might have listened to what I had to say, but not really heard me.
After 5-7 attempts on my part, I considered them a lost cause. And they'd have to learn on their own. I was probably giving them too much respect.
I'd say, let this colleague be. If you still have to provide PRs, then just provide it on Approve/Not approve basis. If your manager requests that you more specific, then provide your honest feedback and kick it up to the manager to decide whether to approve or not approve.
But if you manager is unwilling to deal with this problem, maybe explore your options
I agree, this task should fall squarely on your managers(or your colleagues' managers shoulders)
This sounds like a case of another manager downloading their responsibility.
The problem is some managers do not have the skill set to review the work, then they throw their staff under the bus when they are told that a team members work in not up to par. Usually by telling that team member "So and so says your not..." instead of listening to your opinion and then investigating the situation and dealing with it without bringing your name into it.
It's a tough situation, You care about the company but don't like being the bad guy. If You don't deal with the problems there is a chance things will blow up.
Depending on the size of the company maybe You can request being moved to another team, or put in for a promotion, your already doing the managers job from the sounds of it.
Mostly, the people who had a hard time responding to constructive feedback were young. They might have listened to what I had to say, but not really heard me.
After 5-7 attempts on my part, I considered them a lost cause. And they'd have to learn on their own. I was probably giving them too much respect.
I'd say, let this colleague be. If you still have to provide PRs, then just provide it on Approve/Not approve basis. If your manager requests that you more specific, then provide your honest feedback and kick it up to the manager to decide whether to approve or not approve.
But if you manager is unwilling to deal with this problem, maybe explore your options