B&H Photo have a well written write comparing the three cameras for video purposes.
We generally agree with this article’s conclusions and find it to be a fair and balanced article. The FS7 is better in many but not all ways for video but clearly is not the winner in the size or price department. As many of us are on limited budgets there is an extra appeal to the Sony A7r II which can produce great still images.
Do check out their article: Sony Head to Head: a7 Mirrorless Series versus the FS7 4K Video Camera