Okay, so I think the danger with this strategy is that you’re opening your gang up to the Sisters. A gang can only do one thing per turn but also works as a ‘mobile thug’ so if you’re clever you can work around them until you can snuff them out. Thugging up a gang’s HP is a good idea but once it’s assassinated in one move that’s a lot of resources gone in the blink of an eye! In fact, a daggered up master thief is a good deterrent because it gets costly to keep hiring thugs. Combined with a gang you can make a good dent on your opponent’s dominant gang strategy. What’s more, the dagger upgrades get you close to a second gang which is really handy but trickier to reach than anything else. I love the Safe Cracker upgrade though!
I’ve found with this game that a good strategy (thugging master thieves in, cheap mass urchin evictions, gang stomping) can look unbeatable but I think there are definitely ways around most of them.