End crystals and TNT explosions do same damage regardless of difficulty for entities except players

The bug:

End crystal and TNT explosions do same damage regardless of difficulty for entities like zombies. This is bad to practice Crystal PvP on buffed zombies.

Normal damage:
Peaceful: 0 hp / 0 full hearts
Easy: 43.5 hp/ 21.75 full hearts
Normal: 85 hp / 42.5 full hearts
Hard: 127.5 hp / 63.75 full hearts

Bugged damage:
Peaceful: 85 hp / 42.5 full hearts
Easy: 85 hp / 42.5hp full hearts
Normal: 85 hp / 42.5 hp full hearts
Hard: 85 hp / 42.5 hp full hearts 

Steps to reproduce:

1. Set the difficulty to anything other than normal, such as hard, peaceful, or easy.
2. Spawn an end crystal.
3. Observe that the end crystal does the same damage as it would on normal difficulty on entities like zombies.

Expected behavior:
The damage from an end crystal should do the same for entities like mobs as for players.

Actual behavior:
The same damage that end crystals do on normal difficulty is the same as on other difficulties on entities like mobs.