The Engine could "ignore" Provinces and go for triple-Silk road turns. It should be able to get at least 4 Silk Roads. The Slog, especially when attacked will not be able to catch a lot of Provinces. It will spike one every now and then, but it won't be able to end the game on an early win. So denying the Silk Roads must be the way to do this - if there is one. Even for the Engine player Silk Roads will be better than Duchies, plus, the Enginge can pick up those Provinces later on while the slog cannot.
In fact, that Margrave "attack" actually helps the Slog player - and it does help a lot more than I thought at first. You're still guaranteed to hit $4 and you can play a Shanty Town, a Smuggler or a JoaT or you have at least $5, sometimes $6.
Since the Silk Roads are so important, I think, you have to rush them and prioritze them over Harems once you've got doubleJack. They will be worth 5-6 VP each.