Why doesn't it seem right? Your first play of Jack, and maybe your second play of Jack, are simply replacing Shelters with Silvers. You're also cycling much more quickly, especially if Jack collides with Necropolis or Forager, and Jack itself boosts hand value by drawing up to 5 cards, which again is an exceptional combo with Necropolis and Forager.
well because silver is an awful card in a highway engine, and you only want it really early, so buying one silver instead of Joat, which will get you even more silver, but kicks in delayed seems preferable.
I was also going to make a point that forager/JoaT is less likely to hit 5$ in turn 3/4, then I got curious and wrote a java program simulating it. so forager/silver has a 57,8% chance to hit 5$ once, 0,7% chance to hit 5$ twice, and JoaT/forager has 46,6% chance to hit 5$ once and 6,7% chance to hit 5$ twice... unless i made a mistake, but that sounds reasonable. so it's not that likely to matter, but whenever it does it's probably game deciding.