One illustration of this is that in Goblet of Fire, there is a point where canon!Harry on a broomstick faces a dragon called the Hungarian Horntail... which in Ch. 16 of Methods is said to breathe fire quickly and accurately enough to melt a Snitch in midflight, implying that canon!Harry would have gotten roasted in an instant if he'd tried the same thing in this universe.

What if, in accordance with the Tournament's goal of providing an interesting challenge and spectacle without massacring all competitors, the dragons were actually subdued or sedated in some less-than-obvious way?

For that matter, the ability to melt a snitch (which is small, apparently made of gold which has a relatively low melting point, and not specifically designed to be indestructible) isn't the same as the ability to kill a well-prepared wizard.