Android 16 is one of the most powerful Artificial Humans created by Dr. Gero. Despite being created before Androids 17 and 18, it is considerably stronger than its successors. In the original series, it is never explained why 16 is much stronger, but it is implied that there is something “wrong with him” given his personality.
In any case, 16 doesn't like violence, so he doesn't fight much in the Cell arc. When Android 17 is at the mercy of Cell and almost absorbed, Android 16 interferes by punching Cell and freeing 17 from its grip. Android 18 asks why they landed, and Android 17 says there's no hurry and that they'd better enjoy the trip. Then, Android 17 asks Android 16 if it doesn't want to tell you or if it's the loud and quiet type, but Android 16 still doesn't say anything.
Fortunately, Android 16 finds Goku after the fall of Muscle Tower, so Goku has the support of Android 8, which fights to protect his friend of 16. In the anime, Android 18, Android 16 and Krillin try to fight Cell to no avail, but Bio-Android beats them all effortlessly. Denying it, Android 18 believes that Vegeta could have pretended to be weak when he fought before, but Android 16 claims that he would have no reason to do so and that something changed in the past few days. Cell makes fun of Android 18 and Android 16, saying that they can't escape it and that, thanks to absorbing Android 17, he even surprised himself with his new speed. Android 16 and Cell had already fought in the manga when the movie 7 was released in July 1992, but this hadn't happened in the anime yet, nor was it close to doing so. The point is that it is a valuable addition to the Android list, since it has defeated many and is capable of consuming whoever it wants. After 13 broke Trunks's sword and withstood all other aggressive attacks, Goku barely managed to destroy it creating a spiritual bomb and then absorbing that power into itself to destroy the devastating superandroid with one blow. It is clear that Android 16 was one of the strongest Artificial Humans created by Dr.
Despite not being able to defeat Cell on its own, it was able to protect its fellow Androids from its evil counterpart. It also proved its worth by helping Goku defeat Superandroid 13 with a last desperate effort.
