empire halberds

so i have been looking at alot of empire army lists and i always see these guys as detachments hardly ever parent units?

is there a specific reason for this the pros for me of the halberds outrank that of a swordsman. we are hitting on 4+ with most of our core choices anyway so that ws4 to me becomes a bit pointless where as a group of str4 halberds with shields for the same price seems pretty tasty considering they can now fight in two ranks!

so basicaly am i missing something here for me being able to hit on a 4+ and usually wound on a 4+ is better than a 4+ 5+

obviously theres the fact of initiative but were usually hitting last anyway ...?