There are many (complicated and domestic) methods of hiding your identity.
Yeah, in fact, meshes are a pretty shitty way of doing so, since you'll want encryption anyways and it's not exactly hard for a malicious person to set up a node that stores its traffic / performs MITM attacks.
It is indeed not a good way when all you want is hiding your identity. However, it does make it considerably harder to tap all of the network. Currently, the NSA etc have to monitor the key nodes in the network. When the network is meshed, there are no key nodes in the same way as there are now. This in itself reduces the possibilities there are for surveillance, as the only information you can decrypt is the information you have.