The is just so unimaginative that I can't believe you've ever seen the inside of a large operation. How are you going to sniff traffic that's communicating on a private network? And how does trivial sniffability not extend to all unencrypted traffic, ergo nearly everything is public? That's a totally useless definition and misses the point entirely.

Your point #1 is totally unjustified: you don't know what you could learn by e.g. looking at a data structure used internally. #2 shows that you are unable to answer the question of which of Dropbox's incentives are satisfied by doing this.