Which contrast is grammatically accurate?

Mudari Takhfif and Lan

• لَا يَكْتُبُونَ keeps the nūn here, while لَنْ يَكْتُبُوا removes it.
• Both لَا and لَنْ always remove the final nūn.
• لَنْ changes every imperfect into past tense.
• لَا always creates stronger future negation than لَنْ.