Teemo is annoying in lane, but I wouldn't say broken, because of how Teemo works as a champ. If he gets fed, he's not really going to carry.
Pantheon falls off because, whenever you look at graphs of his winrate overtime, it decreases significantly as the game progresses.
What's happening now is that he has an extremely high winrate, so even as time progresses, the winrate is still high.
For instance, if he were more balanced, and his winrate early game was 53%, his lategame winrate would be something like 43%
But right now, his winrate from 0-20 min is an absurd 59%, so, even as his winrate decreases over time, it's still a hefty 49%
If you look at KR, Panth has an early game winrate of 54.4%, which eventually winds up to 38.96% at 40+min
A separate issue would be the snowbally and faster games which all benefit Panth.