Which of these is untrue--
1) I am very susceptible to being derailed commentary
2) I am incapable of being derailed by outside commentary
Don't look at me. Answer it for yourself.
Okay, I will answer it for myself. Yes. I mean both. And as I have said before I no longer make changes unless someone is going to pay me to do so.
When you're starting out it's natural to ask "How am I doing?" Unfortunately, people will tell you. Then you will begin writing to suit them.
This happens all the time with agents. They will make a casual, unserious comment and then you try to fix the project for them so they will--PLEASE!-- represent it, and after you finish turning your story into theirs, they're not interested any longer, or that market's changed, or they were in a car wreck (yes, that happened to me, not the wreck that was the agent) and are out of the office for 6 months.
A writer needs to learn how to protect themselves and their work. If you enjoy being critiqued and trust the person, then maybe it's helpful. If having comments makes you doubt your choices, maybe you should wait until the project is completed before you let anyone read it. Then if they have complaints that you left something out, you may be able to point to the section they glossed over where everything was so cleverly explained.
Write your story, not theirs.