I think it's as you say. Lemmy's growth is going to happen in waves, until it has reached a critical mass that sustains its own "weight", in terms of growth.
You have to remember that this is no commercial platform, with little advertisement, which is made by its own users. Growth is bound to be slow, at first.
If you're already using a tiling window manager, what is the point of tmux? Genuine question, as I often see people here doing this with WMs such as sway, hyprland and the like.