This behavior of mixed group of biters feels counterintuitive to me. I would expect units of different kinds to have independent pathing: fast units get to the destination quicker than slow units, fliers take direct path while walkers have to walk around. Maybe that’s just my RTS background talking.
Thats a different concept. If you have two unit groups, then it will work as you describe.
If you have 1 group with mixed units, it would be weird if they split up and arrived at different times.
I think we have differing images of what a “group of units” is in our heads.
In this context, I perceive Factorio to be similar to an RTS game like Starcraft, where a player can drag-select a group of units on their screen and then right-click on an enemy base to send them to battle. In Starcraft, units of different speeds/movement capabilities would behave independently and would, yes, arrive separately. This provides a challenge for the player, but also gives consistent and predictable results of what will happen when you command a group of units to go somewhere: they will arrive as fast as they can regardless of what kinds of units were selected.
In an 4X game like Stellaris a fleet of units would be behaving as you describe, but that would require the player to explicitly designate a selection of units as a “fleet”.
In Factorio unit group refers to a special game object, the 'unit group'.
This group does pathing, and members of the group do simple and efficient logic to just follow the group position. This helps reduce UPS usage for 500 biters trying to cross a lake. Just 1 pathfind is done for the group, and the 500 biters just follow the group.
Selecting units and what happens in Starcraft isn't specifically related.
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