Nobody hates casual players; they probably dislike, myself included, the way arguments are constructed.

To be able to provide pertinent feedback in general, you do need to have a good grasp of the class/ role, played at all levels of difficulty in a balanced, productive way.

Some tips on how to actually provide constructive feedback:
Use “I” statements.
Provide actionable feedback.
Include positive comments where appropriate.
Make it a conversation.
Maintain a friendly tone.
Be specific.
Be empathic
Avoid assumptions
Now, how many of those "feedback" topics check all of these marks?