Nerfed Chancellor Vassal is actually considered a pretty weak card.
The problem with Vassal is that it costs you actions whenever it fails, and you can't really predict how many times per turn that's going to happen, so either you prepare for something roughly around the worst case scenario, in which case your deck works but you spent a bunch of time acquiring the extra +actions that mostly are just going to sit there doing nothing to return that investment, or you prepare for something more like the average scenario, in which case your +actions are getting spent efficiently but your deck doesn't work half the time. It similarly costs +cards as well. Even when your deck contains almost exclusively Action cards and you can support many Vassals with only a couple of extra villages, it is often a significant drawback that you don't get to choose the order in which you play them. Conspirator doesn't have any of these problems, you can just add it to any normal engine deck and it'll just be an actual double Peddler, and 5 Conspirators actually cost less than 5 Vassals + 2 Villages.
Also, terminal Silvers are godawful. Regular Silvers themselves are not that great, because each Silver you add makes it harder for your engine to work — you need more draw to be able to draw your whole deck and more villages so that you can play all the draw, and that takes some time to acquire and you'll have a bigger risk of a bad draw the bigger your deck is. It's often necessary to get 1-2 Silvers in the early game so that you can hit $5, but you really want to stop buying Silvers and start spending your buys on engine components as soon as possible, and often you don't even want Silvers for free in the mid and late game. Terminal Silvers are that, but way worse, and you should actually be trashing them with Sentry more often than not if you find yourself having cards in your deck that are practically just terminal Silvers all the time.