Methinks a few of our colleagues need to have a refresher read up on performance.
First, nothing is guaranteed, as such. If the actual conditions on the day replicate the certification presumptions, and you fly it like the AFM suggests, then you should get something like the certification performance. But things can get considerably worse than what was presumed at certification and the results can get a bit nastier.
Heavies are not too bad as a lot of work goes into getting certification numbers and the operational procedures are a lot better for pilot longevity.
Lighties ... you have to be joking. The main reason we don't have smoking holes all over the place is that we don't have many serious incidents at low level and, in the main, terrain tends to be reasonably benign. Anyone who thinks that lightie certification performance is in the same paddock as heavies is a little off the mark, I fear.
The only requirement of great note is "don't crash". You have a far better prospect of achieving this in heavy aircraft operations than in light ....
For those who don't know Mach E Avelli's background, he has a lot of runs on the board in a lot of different aircraft and his observations are worth listening to.