As far as I was told, snap sandboxing only works with a specially-patched (and apparmor-enabled) kernel [1], though I am not sure what the current status is.
I would like to know what's better implemented in snap, it seems this is simply a case of most applications requesting a r/w permission in the home directory. It might get complicated sandboxing vs code without that, don't you think? Or at least lead to a subpar user experience.
I am hopeful it will improve, though. Sandboxing needs to become the default.
[1]: https://web.archive.org/web/20170615042616/https://github.co...
Edit: Similar echo here https://news.ycombinator.com/item?id=18180877