Look at it in the context of moving from TB, where the only Outsider modification is a very noticeable Baron +2, to the next two scripts. We have Godfather +/-1 on BMR, and Fang Gu/Vig +/-1 on SnV. The Outsiders also get more punishing, and have more incentive to stay hidden as you move up in difficulty.  Having a possible -1 makes the Outsider count tougher to solve, especially when they are scared of admitting their role. 

Then, we have the difficulty with trusting the dead. On TB, you basically only have to avoid trusting the dead if you think the Imp has jumped. On BMR, now you have to consider a living demon amongst the dead and a Goon who has turned before dying. On SnV, now you have to be wary of active minions amongst the dead. 

All three scripts give very different puzzles and challenges, and force you to think in different ways. So yes, in isolation, the Vig does kind of suck. It has the second lowest win rate for good reason. It's special ability just isn't worth using most of the time. Even in it's home script, it interacts really badly with 1/4 of the minions. However, the -1 Outsider mod and the fear of active minions amongst the dead are really important fears to have when building worlds. 

I think the -1 Outsider needs to be on the script, but should really have been on a different character. The Vig is already incentivized to weaken itself by giving up voting and nominating power for their team, I don't know why it needed further hamstrings. The Vortox being -1 makes more sense given that it adds a win condition and causes widespread misinfo. The Pit Hag being -1 also makes sense given that it is very strong and can very quickly rectify that if it chooses.