Is this an evidence backed opinion or just anecdotal? I does not make sense to me, because I think attempting to speak in a language helps your brain form the new linguistic machinery that is also used in listening. I think language development is a feedback loop between speaking and listening.

My anecdote - learning Mandarin, which is tonal, is absurdly hard before you develop an ear and tongue for tones. I think trying to practice speaking in tones helps to then hear them, because you understand the sounds people make better. How they abbreviate/slant or modify tones based on surrounding tones - why? Because it feels better in the mouth. So until you experience that, you won't understand slant tones and such.