They are two totally different types of pain, a piercing is a sudden sharp pinch that's over in a second. A tattoo is like a million or more sharp quick in and out, over and over stabs/pricks with a needle (like a shot that doesn't go all the way in.) The tattoos hurt longer because they take a lot longer. Neither is that bad in my opinion. I have 4 piercings in both ears, 1 in my nose, my belly button done twice and I've had my tongue pierced 3 times now, and I have 2 tattoos. It's not all that bad if you have a decent pain tolerance.
They are different kinds of pain. When I got my nose done, it was just sharp and quick and over. When I got my tattoo done (half sleeve), it didn't hurt as bad, it just took longer.... it felt like a cat scratch kinda.
I have had my medusa, Monroe, septum, vertical labret, tongue, ears and belly button pierced. But I have 9 tattoos on ribs finger ear cartilage arms collar bone and thigh. I speak from experience piercings are more sore. Tattoos is just like warm scratching.