I don't think you understand how hard it would be to fire a MD or forge gun from a dropship. Sure, forge gunning and MDing is easy now, but you are on solid ground with complete control over how you are moving.

In a dropship you are constantly moving and tilting and rocking in directions you have no way of predicting. I don't know your experience with turrets in a DS but if you've ever tried firing a missile turret from a DS you'd know it is a challenge. The ship is constantly shifting and maneuvering unexpectedly, some times in minuet ways and sometimes in extreme ways, and you have to try to compensate for all of it on the fly. Also, turrets are built into the dropship with a view mode that is made for this type of combat and you have a passive zoom mode that puts you right at the end of the turret and a very good zoom feature built right in that helps you even further.

Something else you may not know about shooting from a DS you cannot shoot anything directly in front, behind or below it. Your rounds hit the ship. And as most of us who've flown DS's for a living before know, ANYTHING that hits the DS no matter what it is has an impact on your flight path. Missile turrets jar you sideways, blaster rounds slowly careen you sideways, forge guns hit you so hard your whole craft rocks like a ship in a hurricane, swarms (enemy only for obvious reasons) throw you to the side, AR rounds make you drift off course, MD rounds try to tip you over.... I can go on to cover them all, but I really don't want to. Point is, you have severe blind spots you cannot fire at when in a DS, especially if you were to be actually IN the DS and not hanging out of it in the turret mount (get a close look the next time you see a gunner in a DS turret, he's not all the way inside the hull).

On another side of things, even though a normal weapon typically has zoom just like the turrets, have you seen a MD in ADS view? It's terrible, utterly useless to most people who pick one up. It has a low zoom fidelity and the markings on it are a mess to try to use when trying to line up shots. Not to mention that MD's have an ungodly low ammo carry capacity, so they may spam for a couple clips, but then they either have to sit there and fire off their sidearm ammo too or head to a supply depot and restock. Mass drivers in a DS that is constantly on the move aren't going to be able to do much more than spam random area denial rounds at large groups from a DS unless that DS is flying very low and very stable. And if it is, it is the subject of every gun in the vicinity, everything from AR's to flaylocks to MD's to AV gear because there are people in there that can be shot out who cannot move unless either the DS moves away or they jump out. There is no strafing in a DS to avoid bullets. If the pilot can keep you safe, wonderful. If not.... then you can either jump out or take a death.

Have you seen a Forge Gun in ADS view? No you haven't, because there isn't one. Forge gun sniping is moderately challenging from a distance when you are able to fully control your stance on solid ground because, as we all know, under normal circumstances solid ground tends to feel.... relatively solid. Now picture a forge gunner trying desperately to take shots from a DS that is always adjusting it's pitch and yaw with no means of zooming whatsoever. Sure, the DS can hover. Which makes it a giant floating target in the sky that everyone can see and WILL shoot at with whatever they have on hand.

TL;DR: You.... really don't have any clue what you are talking about. Not to be offensive in any way, but you just really have no clue.