Can an Armorer Artificer wearing Guardian-model Arcane Armor cast a somatic spell without holding tools or having the Warcaster feat?

The Guardian model described in the Arcane Armor feature of the Armorer Artificer includes "Thunder Gauntlets":

Each of the armor’s gauntlets counts as a simple melee weapon while you aren’t holding anything in it…

If the Artificer holds tools for a material component of a spell, the description above doesn’t apply. However, if the armor itself is used as the focus (assuming it’s an Infused Item), the Artificer is effectively holding a weapon in each hand.

To deal with this, must the Artificer have taken the Warcaster feat (to allow performing the somatic component of a spell while holding a weapon)? Or can the Thunder Gauntlets be considered "sheathed" when not attacking with them?

(Note: All Artificer spellcasting requires a material component, so performing a somatic-only spell is not an concern.)