Beyond the (slightly behind trend) enthusiasm for blockchains Session is the same punt on contact discovery as lots of other systems that went nowhere. This works great for little secret decoder ring cliques but doesn't actually secure real people's day-to-day messages due to lack of discovery - your local butcher and the guy your sister went to college with never find out that you have the same secure messaging app, and so their messages to you aren't secured.
In contrast to your disinterest in convenience features, Session does have a bunch of things that presumably its principles felt were non-negotiable but clearly harm security. The "Open Groups" feature for example is basically "Eh, this is hard, we give up" for larger groups (500+ people). No end-to-end encryption and you're given either a moderator tool that doesn't work ("Ban" pseudonymous people who can for zero cost just create a new pseudonym) or one that's onerous ("Invite" everybody manually).
In contrast to your disinterest in convenience features, Session does have a bunch of things that presumably its principles felt were non-negotiable but clearly harm security. The "Open Groups" feature for example is basically "Eh, this is hard, we give up" for larger groups (500+ people). No end-to-end encryption and you're given either a moderator tool that doesn't work ("Ban" pseudonymous people who can for zero cost just create a new pseudonym) or one that's onerous ("Invite" everybody manually).