But all of the modes of transport you have mentioned are vital for space exploration. Most people think that a space program\'s job is simply to build rockets. It is not. It is about designing ways to travel and explore other planets. Space itself is quite boring...
Actually in some situations that is practical. Stick the fire warriors up front, rapid fire rounds, allow a charge, fire warriors will (hopefully) flee after minimal casualties, use bonding knife to regroup them, charge with the kroot to mop-up.
Sisters of battle wouldn\'t be up to marine standard... But they are under powered. Guard on the other hand... They\'re far to good to fit with the fluff. If they were altered in such a way that they represented elite regiments however....