Mobs are difficult to hit with sword without them getting a hit first

Expected behavior:

Swinging a sword will give a good chance to hit the mob before the mob hits you.

Actual behavior:

More often than not, the mob will get the first hit. Seems to happens especially with spiders, but happens with other mobs too.

Steps to reproduce:

1. Spawn a bunch of mobs
2. Try to hit them without getting hit first