Forgot to mention his poison has 100% longer range than the graphics show, and it's DoT with no debuff on you.
Uh, do you even play Singed? His poison trail, while definitely a little blurry around the edges, is by no means twice as long as the visual. It also has a very clear visual debuff, a large glowing purple drop of poison hovering over your head. Singed almost always loses lane, he just makes up for it by hard farming later. His damage is minimal if you get a negatron cloak. Buy mercs and you deal with both his damage and his slow all at once. Proxy farming is only a pain when you have 0 wave clear, and basically all viable tops right now have wave clear. He has average CC for a tank, and his passive is only strong if he gets tear>ROA>IBG, but then he is relatively squishy since his passive only gives health. He is easily kited by anyone with a ranged slow (Ashe is actually surprisingly good at this, it's kind of her thing), and even harder by anyone with hard CC, because all he can do is run at you. If he runs away, don't waste your time chasing him, finish off his allies and then shove towers.