I don't think that etymological note in sense 1 helps much.

@@ -20 +19,0 @@
-<s_inf>derived from adjective 無し</s_inf>

Not quite true, many words have no traceable origin of any kind other than themselves; in Japanese this actually happens far more often than, for example, in english where most words have a traceable history in some combination of semantics, morphology, and phonetics. In contrast to this, every other 五段 verb, noun and particle shows little to no such alterations.
Now, here, the information the note provides is both a distinction and a connection in between sense 1 and 3: a reader looking at this entry, or even finding the variants separately, will surely make a connection between them as they look the same, sound the same, and the meanings are notably similar; the aim of the note is to clarify what that relation is rather than to simply leave the reader to their speculation.

In summary, since a shared etymology among the senses is already strongly suggested, the note is there to clarify what that etymology (if any) is to any reader who might be left wondering.

@@ -20 +20 @@
-<s_inf>derived from old adjective 無し</s_inf>
+<s_inf>derived from adjective 無し</s_inf>

無し: derived from 無し

How is it helpful? All words have an etymology, that doesn't mean they all benefit from having notes on it.

I do not see how it would be confusing, it states that the nominal-class suffix spawns from the old adjective of proposed sense 3. Could you elaborate?

That note on sense 1 is not helpful, only confusing.