Okay that's fine, downvote me for making an obvious point that disagrees with you.
A "snowballing" champion is designed to have significant power spikes by out-leveling their opponent. These are more often "mid game" champions because as long as they are able to gain an early level advantage they can beat their enemies before they reach the level cap and their opponent is able to catch up.
The alternatives are "early game" champions and "late game" champions. Early game champions are more often able to bully mid game champions which keeps them from getting out of control. They have higher base stats and do not scale as well. Late game champions are more often item dependent. If they can survive long enough they will most likely be the strongest.
And of course with 134 available champions, it is ridiculous to attempt to divide all of them up into 3 categories. Many champions have differing degrees of strength during each phase of the match. Some scale consistently throughout the whole match, others are early and mid, some are mid and late, others are early and late. Furthermore the outcome of any given match is even more difficult to be determined when a team is comprised of a combination of 5 of the aforementioned snowflakes (no pun intended, ... well, maybe a little intended), and then there is the actual knowledge and skill of the person sitting on the other side of the keyboard.
So in summary, any champion who is infact "snowballing" will be "out of control" until they are no longer "snowballing"