Can someone please explain how the new units are supposed to be used?

The Doom Walker for example, it has higher speed than the other long range units which means it quickly moves to the front and take the first hits in a long range fight. Personally, I think this is a bad trait for an expensive unit that takes a long time to build. The other long range units have movement speeds that make the hit order helicopter->hailstorm->artillery->railgun tank which is perfectly fine, the most expensive units die last. How is the Doom Walker supposed to fit into all this?

The same goes for the other two new units, their movement speed and attack range does not fit with the other short- and mid-range units.

Are the new units designed solely for use in global domination (where unit range and speed means nothing), or did someone mess up when the new units stats were set?

An explanation would be much appreciated.