Īm I missing something? I can't see any drag function NOR I can take units out of commander control and place them in the map.
WHY this game doesn't allow at all to do it despite the game saying that u can merge units? Is it telling about exchanging units between commanders? That's not merging units, it's reinforcement exchange.
Some total war even allowed to do it with different unites and just average down the level of that unit. In other Total war u just Drag the unit into a similar one unless they have different experience