I never really noticed a balance issue with shotties either (sorry, i forgot who said that). It was merely the aliens worked as a team to ambush and kill them, and in general alien teams arent good at that. Yes, i know the aliens are supposed to be loners and all that jazz. But think for a minute. All that is needed is a slight change in tactics.
Scenario 1: One skulk down a hall vs a marine
rine wins, hardcore.
Scenario 2: One skulk at end of hall. Rine at other end. Extra skulk somewhere in middle
Strat: Skulk one pops in and out, parasiting the marine for his sneaky teammate. Rine becomes angry/annoyed, and come to get said annoying skulk. Skulk two falls upon hapless rines head and proceeds ingestion.
Outcome- simple teamwork > marine.
This strat works well with more than one marine as well, mostly because many marines arnet good at close range, even with a shotty when surprised.
And that is the key. Keep the mainres looking at every shadow and they miss the skulk in the bright lights because they are looking the wrong way. The bait can also be other lifeforms, like gorges, fades, whatever.
This strat does lose its effectiveness later in the game, especially when the marines have heavys. THis leads to the other portion of the strat. same idea, same setup.
Add a fade up close. Which will the mairne go for first? The fade? or the pesky little skulk that "can't hurt me I'm a heavy!!"?
I think we know the answer. So long as the aliens have the jump on the mairnes, they win, which is why i prefer movements (for silence) and sensories ( for sof) first. Admittedly, these need to be placed at the game start, but they come as a surpries for the marines.
So, I have clearly presented my ideas, but I may have missed the point.