Create friendly feedback for a freelance writer. Mention that you have noticed that the research is not in depth, the sentences are longer and general style has changed.

Hi just wanted to give some feedback and get also get your point of view. We noticed some changes in your writing style for the past few articles. The research is not as in depth as it could be, the sentences are a bit longer than they need to be, and overall style has changed. Is it possible that you are trying out new things or tools perhaps?