It doesn't matter what you play as long as it's within the meta. For example..... upcoming items are designed for Fighters who build tank items, and Champs who need their first auto attacks to be strong to succeed. As long as the champ you choose is within that meta, If you become 200+ game proficient with it, you'll probably get to a 60%+ win rate with it. If you deviate and change champs during that time, you'll lose some skill with it as you harmonize with a difference skill set.
I don't think Teemo is currently meta, because I generally dominate him, and no item changes are really catering to him more than comparable champs.
is a pretty good climber with very few counters atm. If you master her as a Top..... you'll be monstrous.
If you master
as a Mid, you'll probably easily get to Gold.
If you master
as a jungler, you'll probably be able to get Plat.
If you master
as an adc, you'll probably get to Plat.
If you master
as support, you can probably get to Plat.
These champs are rarely influenced by item meta changes, and all are generally benefited by current runes and kit access versus counter-playability.