Leather Armour add Inventory Space

Leather Armour gives extra inventory, hot bar, and off hand slots per piece. leather armour give lots of options as there are in fantasy art lots of pockets on leather armour and it would make it unique and worthwhile to use.

i would add hot bar or off hand over just inventory to make it more fight based so its not just for doing builds or moving resources

Leather also gets effected by a group of effects like regen(Regains durability), Fire Resistance(Immure to losing Durability to fire), and Poison(Loses durability)

also the following post has another way to buff Leather.

https://feedback.minecraft.net/hc/en-us/community/posts/34275006670221-Attack-Speed-Effected-by-Armour-Fix-for-Combat