You're hitting on a lot of common experience with your articles, which is great!
I think the biggest thing you're saying well here is: "swallow your ego, listen to and learn from the harsh feedback"
Which is a tough thing to do, whether it's about getting better at photography or basketball or cooking meals.
In defense of Flickr and 500px: Though it's a fun time waste to scroll though and fav stuff between uploads, these social media sites can be channels for giving and taking feedback:
1. There are groups on flickr for strictly for harsh critiques.
2. It's a great way for me to see my friends' work immediately, so as to be ready to have conversations about the shots next time I see them in person.
3. Location scouting. I can see a variety of images from an upcoming location and critique others' work so I know how to do better/what to do differently when I'm at a certain spot.
4. Not only with my local friends, but I also make online friends who give me good critique, and respect my opinion when I look at and comment on their stuff.
5. If you do a little tagging and describing, you've got a good base to copy from and paste to description fields and keyword fields in stock upload pages.
So, if used intelligently, Flickr and other photo social media sites can be of great value specifically to my microstock photography skill set.
I still agree that we should be our own harshest critics, though.