If the student can spare the money, then a teacher is usually better. I just take conversational lessons, so it isn't necessarily the teaching aspect, but it's more efficient because you can speak in your target language the whole time. But speaking and listening to a native speaker is always beneficial, whether it be a paid teacher or a language exchange partner. The paid teacher arrangement is more of a business relationship, so it is easier to consistently schedule lessons, etc. Organizing consistent language exchanges where both people are on similar levels can be challenging, also.

Totally agree with you