Prior to LH I usually played the game with a large stack of powerful heroes. It was a little clumsy, but not too hard, to move items around between heroes in the big stack  to optimize use of those items and manage the weight/burden penalty issue.

With LH I find a single stack of heroes too weak, and am playing with several stacks of trained units each with one/several heroes leading them. Each stack collects items during questing etc but there is currently no comfortable mechanism for transfer and optimization of items across Heroes in different army stacks.

My "instant" and completely "un-thought out" solution is a one-off location on the screen built by the sovereign like a city, to which heroes in army stacks can go without leaving their army, drop some surplus items off in a chest, to be  later picked up by other heroes in other army stacks as they drop by.

Alternatively two army stacks with heroes on the same game tile could have an extra dialog box to allow any hero in one stack to trade with any hero in another stack.

I have to say though that I don't really like the current trading screens. Using them seems clunky.