but they have one problem - they are micro intensive and when the numbers become bigger and bigger, you need a lot of skill to manage all of them.
It's true but what moving units are not microintensive? It's kinda same for all. You still have to pay close attention to your hmg and I don't think, for example, a King Tiger is micro-unintensive. The KT is slow and a high value target. With this sluggishness in mind you need to be fast with microing it for that very reason and driving the KT is not just driving the KT, it's also managing all the supporting units around it, or it will die.
I say (and you do as well) that micro-intensiveness is foremost a function of number of troops and all movable troops are micro-intensive, so I don't think pinpointing certain units and labelling them micro-intensive is a fair representation.