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.