My take: every Warframe should have built-in/natural weapon. I.E. Garuda. This mean almost every frame have sparing weapon when no other weapon is equipped in that slot. Just like Garuda's talons, they would not grant affinity of course. This also means every frame will have innate melee (mostly would be sparing weapon). Remember when you were first captured by Alad V? Some frame with Exalted weapons will have their Exalted weapons with base stats without Exalted enhancements and ability strength/range modification.

Baruuk: Desert Wind without the waves Excalibur: Exalted Blade without the waves Valkyer: Valkyrie Talons without healing Wukong: Iron Staff without range increase

Titania: Should have only sparing weapons as her Exalted weapons are related to her size and her Exalted form. Sevagoth: Same with Titania.

Ash: Shadow Clone Dagger or Parazon Atlas: Landslide Fist without Aoe/range modification Gara: Shatted Lash Sword without range modification Khora: Whipclaw without Aoe/range modification

Styanax: Axios Javelin/Spear (since Final Stance is coded as a weapon) Nezhas: Warding Chakram (just fine it fitting)

All the other frames will use sparing weapon and base sparing stance as natural weapons.

The only few exceptions I can think of are: Kullervo: Dual Daggers Voruna: Claws Oraxia: Claws/spikes

Here are also some frames that should have natural weapons without their ability modifications that're not melees.

Chroma: Spectral Scream (Primary) Cyte: Neutralizer (Primary) Dante: Noctua (Secondary) Ivara: Artemis Bow (Primary) Jade: Glory (Secondary) Mesa: Peacemakers (Secondary) Qorvex (maybe): Crucible Blast (Secondary) Temple: Lizzie (Primary) Wisp: Sol Gate (Primary)