Fine, I'll humor you.
>If you're using a drop pod as a weapon it doesn't need to be filled.
First off, Space Marines use drop pods to get on top of the enemy. Like, literally on top of them. So they're not being used as a literal weapon. But just to note, I'm pretty sure the thing has a storm bolter or something similar on it so it can either shoot while they fall, or shoot as the Marines disembark.
>...when the individual soldiers at the front lines may be like 1000 feet apart with guns that have a range of 2 miles or so, they're just going to laugh and snipe down the retarded astartes.
No. Just no. Astartes are shock troops. And going fluff-wise or gameplay wise, they don't fight at those kind of distances. They generally do fights at closer ranges, where it's possible for them to run up to their enemy and gut them.
>Also, spess mehrenes do as well against things that can't be horrified or terrorized like orks, necrons, and tyranids, so I seriously doubt they actively go for that sort of thing.
While that's a bit true, they DO fight enemies that can/will be terrified. Such as cultists, traitor guardsmen, Tau, and Eldar. Also, don't forget that not all Orks and 'Nids are souless fighting/killing machines. The smaller, more canon-fodder ones can break in fear/terror or whatever analog applies.