It's hard and scary to give critical feedback at first. You also don't want to damage relationships, especially when you're counting on peer feedback to eventually substantiate your own promotion.

All that said, if you put in the effort to learn and practice giving well-formed, critical feedback, I can almost guarantee the person on the receiving end will deeply appreciate it. Even if it's hard for them to hear, they'll know how it was hard for you to give, too, and most likely they will be grateful to you for it.

Next time, take that risk, and you will be glad you did.