For whatever reason Mojang decided not to have the attack indicator on by default. After seeing all my friends on my server complain about how they aren't doing damage, I realized they had no idea about the charge up added for weapons.

Basically if you spam click like you could before, you'll barely do any damage. You need to wait a little bit before each attack to do full damage. This timer is off by default, but can be turned on in video settings.

I have no idea why they thought it would be a good idea to have this off by default, it's just going to confuse a lot of people.