we should note that not everyone takes extra actions. users would be even safer is vpn + tor is used, and even more safe if simplex is installed on a disposable phone — yet up to 90% of the users don't use vpn and tor additionally.
session includes tor-like system (with actually higher safety than the tor) in the core. thus, in session privacy is on by default, not optionally.
note once again: I'm not saying session is definitely better — both apps have their advantages.