It's not about the value in the response, but rather, an opportunity for them to practice writing out their thoughts and getting corrected for free. I definitely understood your point that they are probably masters in their language, but, what's the point? The point now is to get proficient in Chinese, isn't it?

It's about getting the new learners out of their comfort zone. It's about getting them extremely uncomfortable and pick out their errors in a safe environment.

I'm picking up other languages right now, & I understand their pain.

To learn effectively, the new learner must be willing to put themselves out there.

Case point:

My ex boss, a shipping director who oversees multiple offices in Asia, including S Korea & Japan, has never taken a single paid lesson. He shared with me that he used the dictionary and got his staff to read to him & explain to him how to use the words. He reads the road signs & commit them to memory because he wants to drive around the suburbs. He loves to speak to natives in their languages & he's happy whenever they laugh at him because it means that he's gonna get correction, again!

Be uncomfortable, speak and communicate in Mandarin. Chinese is just the written form. It's Mandarin that you are learning.