Post Death screen

Why do they even give this to us. All the information is not true which then entirely defeats the purpose of it.

Dmg over 11 second. From Kha'zix jumping out of a bush. And getting deleted. From 100%. Sure it was 11 seconds, also I'm sure he only did 15 % of my health in dmg like it says.

Or like mixed Damage? What does that even mean? How do I build to avoid mixed? Is it 10% magic 90% Physical? The opposite?