Trenchant
Etymology
From Old French trenchant, "cutting" — the present participle of trenchier, "to cut" (also the source of "trench"). It began as a word for a literally sharp blade and moved to describe sharpness of thought and speech.
adjective · /TREN-chunt/
Sharp, clear, and forceful — especially in criticism or analysis.
What it names
The quality of a remark that cuts straight to the flaw and leaves no room to wriggle.
Example
Her trenchant summary exposed the flaw in the proposal before anyone else had finished reading it.
Related idea
Incisive is the close synonym; caustic adds a note of cruelty that trenchant doesn’t require.