I am not really sure if this is an issue or intended behaviour.
It took me forever to move to end of a 6Mb file.

Steps to reproduce:

• $ seq 1 1000000 > test
• $ bat test
  Press G to move to end of the file.
  This step took a long time. It seems bat was going through the file sequentially.

Apologies, if this is not the place to ask this question or this is a known bug/feature.