The mass driver is fine the way it is. Hell, in the right hands, it's even close to being too powerful. I'm looking at you, Warzor.
The painsaw is fine. It's meant for anti-construction use, or maybe against big bugs if you have the moves (and cajones) for it. It isn't meant to be useful against Marauders. It's not like it would help you much anyways even if the range was increased. The Marauder Zap still has the range to take out a Painsawer even if the Marauder just stays on the ground. That's one of my favorite things to do, by the way.
Marauders can be taken out if the map allows for it. Basically, you need to stick to hitscan weapons, and possibly the Lucifer. If charged sufficiently, a direct hit with the Lucifer will one-hit an Adv Marauder with full health. Believe me, I know all too well :evil: . Or, you could also try firing it where the Marauder will land.
With hitscan weapons, latency becomes important since the Marauder bounces around like a crackhead on a pogo stick, and really moves along by doing so.
If you are close enough, this makes the shotgun useful. It seems to help me hit those bouncing bastards if I wait to fire at or after the apex of the jump. This allows you to better predict its motion so you can get more pellets on target. And because it's a shotgun, latency and aim don't quite matter as much as range.
If you are using the other hitscan weapons, it might help to lead the Mara a little bit according to your latency. But not too much. It always amuses me when the Sky Campers at ATCS fire a few a few meters ahead of me so every single shot misses.
If you can chase the Mara to a longer corridor, you can inflict some serious damage, so don't forget to chase.
Really, humans could greatly increase their amount of kills if they chased more effectively.