Transparent HTTP caching as a way to avoid leaking metadata is not pro-privacy. It only works because the network is always listening, to both metadata and message content. The reason why people worry about metadata is because it's a way to circumvent encryption (and the law). Metadata is holographic[0] to message content, so you need to protect it with the same zeal content is protected.

But letting everyone have the message content so that metadata doesn't leak isn't helpful. Maybe in the context it was deployed, where pervasive deep packet inspection was only something China wasted their CPU cycles on, your proxy made sense. But it doesn't make sense today.

[0] X is holographic to Y when the contents of X can be used to completely reconstruct Y.