It isn't hard.
What it sounds like here is the classic case of a poor instructor teaching you using a method that works primarily for diesels and large petrol engines, while you've gone out and tried driving a small petrol engined car.
Would I be right in saying that you were taught to get rolling using just the clutch and then adding gas rather than adding gas while on the bite? If so, that method is incredibly unreliable for small petrol engined cars (I think ford might use an anti-stall system for some of it's newer cars, not to mention their Ecoboost engines are pretty torquey on the low end so they might cope better than other small petrols), while most diesels can crawl up some relatively steep inclines using just the clutch alone (at that point I think it's more to do with fuel delivery than outright torque)
Though as someone else mentioned with the horses. Each car has it's own quirks so each car is going to be different to some extent. But gas and bite is a pretty safe method that works across all manual cars, but those same quirks are why just using the clutch to get rolling isn't reliable. Large petrols and diesels in general should have little issue. With small petrols, it's very much a gamble as to whether it'll cope or not.