I never recommend adding glosses based on the meanings of the kanji alone.

@@ -18 +18 @@
-<gloss g_type="lit">brainless</gloss>
+<gloss>blockhead</gloss>

The problem with including "brainless" is that it's an adjective among noun glosses. We could change this to [adj-no,n] but I feel we should change 能無し in the same way, then...

@@ -17,0 +18 @@
+<gloss g_type="lit">brainless</gloss>

脳なし	4327
脳無し	5613

https://ja.ichacha.net/english/脳なし.html (not sure what the source of this is, not eij)

https://www.tv-tokyo.co.jp/broad_tvtokyo/program/detail/202111/26567_202111091730.html
警視庁ゼロ係５　▼９話「最終章　脳なし殺人事件　前編」

https://www.msn.com/ja-jp/lifestyle/lifestylegeneral/悪気なし？女の子が「弟は脳なし」発言/vp-AALO1Oq
悪気なし？女の子が「弟は脳なし」発言

Play Video次の動画:
初めの一歩でドテッ、心が折れちゃった女の子
 Rumble
悪気なし？女の子が「弟は脳なし」発言
お母さんに「私、脳みそあるのよ！」と報告する女の子。「じゃあルーキー（弟）にもある？」と聞かれると、「ないわ！」とキッパリ。悪意はないようです…。

8 examples on reverso: https://context.reverso.net/翻訳/日本語-英語/脳なし

nearly added these as iK to 能無し but I think it could be considered a legitimate, separate word.

not the same as "no-brainer" in English, of course