Actually, by using the equip menu, I believe you spend a turn (1.0 sec I believe) unequipping, and another turn in equipping the item you wanted to equip in the first spot. Using the Inventory screen to equip seems to do both steps in the time it takes for one, so it is faster. And, in all fairness, players should not be punished (be it in turns or menu navigation irritation) for using the equip screen instead of the inventory screen.
I think that going into the equip menu and selecting any item should list all the items for that slot, and an "Unequip (Nothing)" slot at the bottom, so Equip menu users can access all items and options easily. It would be similar to the (u)se menu, except for weapons or armor, and the Unequip option would be at the end.
And yes, just hit enter on the item you want to equip from the Inventory screen, and you will swap right to it (in one turn, of course).