As far as scum size go...
2 scum in 9 is a standard format. I would say that between 3-4 town per scum is perfectly acceptable. So for 6-8 town, 2 scum (8-10 player game). 9-12 town, 3 scum (12-15 player game). 12-15 town, 4 scum (16-19 player game), etc.
Obviously powers change things around. The presence of a Vig or SK instantly add a variable of uncertainty (they hit town more often, but can devastate scum). Cops, Watchers, etc - anything that investigates, are often useless but can power up town quite a bit if successful. Doctor, in a setup without a secondary kill works much the same way but even stronger (no kill night = saved townie + IC made).
In this setup in particular, scum get nothing. They're all Goons. Yes, they get to choose what they face, but even with what we choose things could've broken quite differently. Lynching the Doctor was straight up bad play (although Robz is wrong here... Town!Galz often plays that terribly. I really do have trouble believing claims. My own issues though). And Shraeye shooting town at that juncture crippled town by removing a chance for a town consensus lynch (example to point: I would not have fake claimed if I couldn't lock out the win. Even if I win the debate with Eevee, I get lynched tomorrow).
Yes, the odds of Doctor or Watcher actually helping town are slim, but they can cripple scum when they do. See Ozle's first game as (extreme) proof of this. Excluding the hit by Vig, this broke down to an all Vanilla game. And give town the lynch back that the Vig took, and I don't think town is as dammed as it seemed. I don't think the balance was that far out of whack. Things just broke our way all game.