I think you're mostly right. We (not leftypol but the Left in general) need concrete political organizations, armed or not, but there is a lot of potential in a decentralized, anonymous organization. If we're unified by the same ethic and attitude, we can work as a machine of small, autonomous parts, collectively helping advance our narrative.
We can be, for example, an informal propaganda apparatus for all the people and organizations we care for. S█████ and Corbyn show that this works. Helping the right people and organizations, amplifying their voices, sharing essential propaganda material, spreading shit around, collectively working towards better arguments and rhetorical points, giving an audience to all the independent efforts of left-wing authors, podcasts, magazines, blogs, musicians, comedians, making sure we're always there on every website to give them a view, a share, a like, a good rating. Teaming up during beefs, collectively partaking in character assassination, just becoming such a pain in the ass for anti-Socialists that they will think "it's just not worth the effort" before deciding to attack us. Helping hook up people in need of skills/tools to advance the cause with contacts, with material, with tips, with money, making sure the things the media tries to hide will reach everyone's ears. Let's write FAQs, study guides, reading lists, let's give each other recommendations, guide the newcomers, spread the words of the veterans, and so on. Collectively work towards building an attitude that will translate as a pool of resources that will be there when we need it.
It's not glamorous like thinking of underground organizations and armed uprisings, I know, but it's part of the dull, boring, protracted and absolutely essential information war that precedes all that. If you think only about the revolution and the armed uprising then you're not a socialist, you're a role-player. A socialist should be as dedicated in the smallest tasks as he is towards the big ones, because by defintion we lack the institutional means to take care of shit like that. From boring task to boring task without a loss of heart we will build the means of achieving the things we really want.