The article sharply satirizes the government's policy.
厳しい is a general word for 'strict' or 'severe' in many contexts (rules, training, weather). 辛辣 is specifically for stinging, caustic language or expression.
痛烈 also means 'scathing' or 'severe', but often implies a stronger, more piercing impact. 辛辣 focuses more on the sharp, bitter quality of words.
From Chinese 辛辣 (xīnlà), literally 'acrid' or 'pungent', combining 辛 (spicy, bitter) and 辣 (hot, pungent). The Japanese reading しんらつ is the on'yomi.