I think rushing provinces with jack is probably stronger when an attack like mountebank on the board. Yeah, you'll slow down the jack player somewhat, but not as much as the colony player will get hit. And he didn't ignore mountebank himself so its not like this is an example of jack vs mountebank, but more like Jack and Mountebank going for colonies vs going for provinces.
I think jack solo should get 8 provinces in about 20-22 turns. With the slowdown from mountebank it's likely he got a bit lucky, but maybe not so much. Also I don't like his counting house buy at all. And you're right about the farmlands. It's not an accelerator. Every time you farmland a farmland, you could have bought a province had the farmland been a Gold. It just gives a few bonus points.