Balance doesn't matter.
I know, crazy, right? Give me 5 minutes of your time and I'll prove it to you.
Nuke Ops is not a balanced game mode. A well executed Blitz is basically impossible for the crew to counter. Blitzes fail only because the nukies make mistakes, not due to the actions of the crew. And yet... Nukies don't always blitz. A lot of the time they declare war, even though war isn't the optimal path to victory and they know it. Sometimes they even stealth or do gimmicks, even though, again, doing so is not optimal. Ideally, we'd balance the game so that there isn't one optimal path, but that's a whole different discussion. The take away is this:
When you give players multiple viable paths to victory, they will not always choose the optimal one.
Which means that balance isn't really all THAT important. It's better to have balance than not have balance, but imbalanced game modes can work because we have players who are not just interested in greentext.
So what does this have to do with shadowlings?
The main problem with shadowlings isn't that the mode is imbalanced (although it is), it's that there is only one path to victory. There are no alternative viable paths to victory that are sub-optimal for the shadowlings to take. As a shadowling, you do the same. thing. every. round. You know the meme rounds where operatives decide to try to pose as NAD inspectors? There is no shadowling equivalent to that. Shadowlings can't do that type of stuff. The mechanics force them to bulldoze towards greentext, the exact behavior that is shunned by the community in every other type of antag. No one blames shadowlings for doing it because they have no choice but to do it.
So even if things were balanced it would be a bad game mode. Sure, it would be better if it was more balanced, and balancing it isn't a bad thing, but it's not the thing that is going to ever fix the issues with the round. What shadowlings need is to be able to actually use different tactics like other antags can, rather than being forced into the same thing over and over. If shadowlings had many viable paths to victory, they wouldn't need to always pick the optimal one. The best part is we don't even really need to worry about balancing those paths to make them equally strong as the way things shadowlings do things now. Even if the other paths were objectively non-optimal, players would still choose to use them.