I attended an EA event on Fringe Ideas and Unconventional Cause Areas and the first question we discussed in our groups was: How do you define 'fringe'?
In my opinion, there is little benefit to discussing what we mean by fringe. It's obvious. We all know what it means. Yes, by discussing the definition we gain some clarity, but it ultimately does not help us find or evaluate fringe ideas.
To highlight this over-emphasis on definitions, when the organiser asked us for any thoughts, another attendee proudly declared: "As a philosopher, providing definitions is crucial!" They admittedly went on to provide a clear and concise definition (though used terminology that I am not familiar, like 'normative'), but the definition did not affect the rest of the session.
Maybe I am being naive and missing the value. Perhaps the exercise of defining things is useful in and of itself, as practice for when it is important. But my suspicion is that discussing definitions of everything is more of a cultural norm and/or something that majority of EA people like for its own sake, rather than a truth-seeking tool.
If it matters, I have background in pure mathematics, where I also think formal definitions are over-rated. In particular, definitions are over-rated by almost all non-research students and most PhD students, who have only experienced the skewed 'definition-theorem-proof' presentation of pure maths, rather than the intuition-based discovery that is done by (good?) researchers.
As always, open to disagreement and feedback! There is high chance I have over-looked a key consideration.
Definitional clarity can be helpful if you think that people might otherwise be talking past each other (using the same word to mean something importantly different without realizing it). But otherwise, I generally agree with your take. (It's a classic failure-mode of analytic philosophers that some pretend not to know what a word means until it has been precisely defined. It's quite silly.)
I think that this is very context specific, and will vary quite a bit. I think that it probably isn't worthwhile to spend 30-60 minutes defining "fringe" when talking about fringe ideas. But plenty of concepts have fuzzy or ambiguous meanings, and in those situations clarifying what we actually mean can be useful to make sure we are talking about the same thing (such as 'average income', or 'an EA organization,' or 'private information').
But broadly speaking, I could see your claim being true. Definitions are important, but maybe not quite as important as EA norms and culture implies them to be.