True, but the pinky is smaller and harder to grasp. Not that it can't be done, just requires a lot of practice. Of course, what doesn't?
If you are lifted off the ground, you may be able to kick a kneecap. Or you may be able to strike into the opponent's head with alternating elbows as well as knee strikes.
If not, in the Hapkido I learned I was taught, we were taught to go for the middle finger. We were taught to strike if forcefully, bending it as you force it back. You have a good chance of breaking it (you have to learn how to strike to lessen the chance you will scratch yourself with his fingernail). You reach up with the opposite hand and with a tight grab of the finger, begin cranking it back. The next part is more difficult to describe than watch, but is devastating. If for example you struck with your left hand, you would be grabbing the finger with your right hand. As you crank it back, pivot 180 on your left foot, moving your right wrist in contact with your opponent. His palm will be towards you, bent back painfully. Step back with your right foot, bending your left knee. That forces him down and forward into your right knee as you bring it up to knee him in the face/head.
That may be hard to conceptualize, but when you see it it is easier to follow and learn. Oh, you may have to slack off just a bit after applying back pressure. We also use the same technique for a two handed grab from the rear where the fingers are interlocked. I was showing that to a KATUSA in our office. It was flowing smoothly until I realized I had pulled it back a long ways without him releasing his grip, and I heard a sudden hissing intake of breath. I released it some and he unlocked his knuckles and it all went well again. Well, except for the very pained look on his face.
Actually, I felt rather bad. But he was a 3rd dan in TKD, and a good sport. Also, his brother had studied Hapkido to 1st dan so he understood there was potential for pain and injury. But I learned to be especially careful of showing techniques to non-Hapkido students.