The hardest part about distinguishing what is useful in any given piece of criticism, tactfully given or not, is that the critique is of something that has at least some degree of personal connection to you. You draw something, you write something, that's an expression of who you are, what you hope to be, what you dream of giving the world. And when someone says something is wrong or off, that can hurt.
But just like @dojo said, just because it's personal does not mean that other people's perception of it is invalid. I love your example: you removed yourself from your art and skill, made the critique about what you can do rather than who you are, and because of that you were able to learn and grow. That's an awesome feat.
I can say that, as someone who is very, VERY sensitive to critiques but also crave them, when I give critiques I try to ask myself Three things:
1) Is this thing objectively wrong? Grammar, formatting, color balance, anatomy, etc.
2) Is this thing confusing? If so, am I taking my time to unpack it, or am I seeing it for what it is?
3) Is this boring/off putting/otherwise unenjoyable? If so, is it because it's just not to my tastes, or is it not executed well?
If whatever I'm giving feedback to is objectively wrong, objectively confusing, and not executed well, then I give a critique. If any of those are in question, I might comment and give suggestions, but they'll be gentle and general, if I comment on them at all.
This isn't a bad way to take criticism either. Is the thing someone pointed out - rudely or kindly - objectively wrong, objectively confusing, or not to the standard you want to ultimately reach? Then take what you can from the comment and improve. If not, leave it to the dust and keep doing you.