Soldiers today wear hearing protection when training with rifles, and even during deployment, earplugs were an inspectionable item in some units. Was ear damage and hearing loss as rampant as one would imagine with the levels of exposure to cannon, artillery, rifles, etc. without any protection?

Yes. "Artilleryman's deafness" is a loss of sensitivity in the mid range frequencies as opposed to the more normal high frequency loss.

However other professions also suffered hearing damage. Boiler makers were an example. Mid 19c literature refers to new workers becoming accustomed to the noise after a few weeks, but this was later recognised as industrial deafness. Sorry, don't have a ref to hand for this.