Is there a hotkey to select all units of the same type? For example, you click on one Skirmisher, and select all your Skirmishers on the map?
Or even better, you select a group of units, and then expand the selection to all units of the same type in the map? (e.g. select one Spearman and Skirmisher → select all Spearmen + Skirmishers on the map)