Good job making constructive criticism, although next time maybe point out a flawed gameplay mechanic/champion, as Teemo is a very balanced champion, even when played AP.
Teemo is a ranged champion, which naturally means he can bully melee champions out of a lane, and he can keep his distance, his W was designed to improve his ability to bully out melee champions and dominate his lane, most (if not all) melee bruisers have a gap-closing ability, which can outrange Teemo's standard attack range, Talon for example can use his E to quickly jump onto Teemo, giving Move-quick not much use.
Movement speed when increased is multiplicative, and (most) slows are additive, meaning a Teemo who is slowed with Move-quick activated is still slower than his normal run speed.
As for his Mushrooms, if he is built AP they are his primary source of damage, it is very easy to avoid them, you can purchase an Oracle, or a Sight Ward to entirely counter the majority of his damage.
If you are playing against a Teemo as Shyvana, you will probably lose the lane until reaching level 6, when you gain your gap closer, Teemo is designed to counter melee AD bruisers and you where playing against him as an AD bruiser, if you where playing someone such as Leblanc, Kassadin or Xerath, you would've easily won the lane, Teemo is not over-powered you just do not know how to deal with him.