If a new word like "tension" adds some nuance not present in a common word, then it's an important thing to keep; if it adds nothing but another word to learn, it's better to stick with a more common word.
I agree with that completely; and I think tension adds a lot of key nuance. Most importantly, "tension" points to an experience - a feeling - where "issue" points to a thought - a mental construct. That's a huge difference when it comes to Holacracy practice and what it's trying to achieve. I think using "issue" is likely to undermine some of the biggest benefits Holacracy has to offer. (Although that might only be apparent and relevant if/when you get through the initial practice phase and to a more mature practice.)
As one example (and in disagreement with your last point): for most people, I think tension has a negative connotation - far more so than "issue". And that's the benefit of it. When people feel what Holacracy calls "tension", they typically then make meaning of that experience as a negative thing - they associate the feeling of tension meaning something is "wrong". Holacracy's use of the word tension - with its negative connotations - allows someone to see what happens as a result of tension through Holacracy, and eventually reorient their meaning-making of the experience into something neutral, and break an unconscious and habitual jump from experience to judgment to resistance. Associating the feeling of "tension" with useful results helps people shift from judging that experience and resisting the reality of it, to accepting it and engaging with it without judgment. That's a huge opportunity, and you don't get it nearly as powerfully if you start with "issue".
Curious if others have perspectives to add here as well...