Without access to the rest of the internet a meshnet is reduced to a local area network. Which still has its use cases but is not viable for any global applications such as a cryptocurrency.
Yep.
But there is a useful thing you can do-- have a diverse network connection.
One great option is to use the blockstream satellite feed: it's available most of the world and has no ongoing cost.
Another useful thing you can do is run tor and connect to peers over hidden services, functionally it's like having a second network connection riding over the first. At least any bitcoin-specific tampering with your network connection wouldn't work.
Aside, -- I wouldn't exactly call any of the mesh things I've seen *secure*-- generally they hardly work even when there is no attacker!
Right, so you are Mesh expert and you have examined all the projects and you know this for sure? No wonder Bitcoin is slow if uses a satellite as third party in its centralized pyramid scheme.