Yeah, lack of etr seems like a liability at first sight, but in reality marcus and caprice fill in the gap and I haven't noticed it as an issue in game. Caprice means they can run through and pay in blood, but still only succeed 1/3 times. The threat of Marcus means they risk death 2/3 times if they let komainu fire, and can often lose their rig if they're not careful and faceplant ichi + marcus without enough clicks/breakers/clone chip. The sentries also synergize well together in taxing/bleeding runners hard especially when their precise order/combination is hidden--the threat of assassin(s?) after komainu can be enough to get a jack out, or the threat of komainu (or just any simple etr) after ichi faceplant can get a jackout. This is something I actually found as a benefit of not playing never advance--the runner rarely checks the remotes till they have to, which means when they do run it's all getting facechecked and they have to deal with potential threats later in the server which they don't know whether they are prickly porous or some form of etr.
In the end sometimes you don't mind them stealing an agenda if they have to pay with a massive loss in board position. On centrals this philosophy applies really well (them burning their board position for centrals access--often single access--is definitely a win), but even on remote (especially with caprice) you're often OK with them losing their hand+more for an agenda (or just a chance at one). Late game Project Nisei glues together the tax + caprice + marcus threat to create a hard lock on remote even with no ETR at all on it.
Also, a corollary on this is that caprice usually lives on remote, while marcus is often used for central defense--but extras of each are used to supplement the other side when needed. Worth noting that firing Marcus a lot is awesome, I've strongly considered running Recruiting Trip in order to get a 4th copy of Marcus (compromised by upping interns to 2)--I can't imagine running only 2 copies of MB he's so useful especially in multiples.
tldr; ETR are a crutch. Just rely on Psi shenanigans together with the threat of efficient death and destruction.