After you trash the estates, Jack is pretty much "gain a silver, +1 or 2 coin". Yeah I know spy-effect, but until you green it isn't that useful. Without +action you get slightly above the average coin in your deck. We have a very similar card - Squire and it costs 2 with some sweet other options (like - it's a village) and a very strong on trash effect. This tells me that buying Jack as a slightly more money, lower versatility Squire is pretty bad. But what about terminal draw? Well you can play terminal draw just fine with 3 dead estates, a sometimes dead Jack isn't that bad. Would I give up a free silver to get triple the coin payout? Why yes I would.
This is why I laugh when people say Jack is bad for engines. If your engine needs Silver, it generally needs Jack. Trade your 3 Estates for 3 Silvers (you are going engine, they will line up in not too long), now you have much better odds of drawing engine components AND you don't have to waste 3 coin buys on Silvers when you could be buying engine components (like Village, Warehouse, Herbalist, etc.) instead; as a bonus your buying power doesn't drop. Yeah, there are stronger 4's to open for engines (e.g. Baron) ... but Jack is quite nice for engines that need Silver.