Twitch is really squishy. He only really has the upper hand if he has you by surprise. If you get him alone, he's dead. If you're Cho'gath or Karthas or Ryze or anyone who does a ton of damage instantaneously, he's dead. I've died many times to Cho's feast ability despite having more than half my health. Killing him early game also prevents him from leveling, but if a Twitch is fed, then I agree, it really sucks. Even so, gank twitch and he goes down.
Twitch's range is already pretty low, at least compared to other ranged characters, so nerfing his range will neuter him a lot.
Spray and Pray's range got increased in a recent patch I think because before they changed this, everytime I'd pop it, people would gtfo and I would do no damage everytime. I rarely use it against turrets, and it is unfortunate that it is used in such a way. Spray and Pray doesn't allow for much control on its own, and nerfing range would make it less useful.
While there are some "godly" players who feed early and rush to get things like infinity edge to do ridiculous ammounts of damage before it can be countered, there are also a lot of Twitchs like me who focus on stealth and attack speed and get nearly equal K to D, and there are also Twitchs who have trouble dealing with the low health and just feed. For those of us who don't like to rape but like to have fun.
In short, Twitch seems to do very well under a specific circumstance, but in other conditions, he's just fine and a little hard to use because he is squishy. This is not much different from what I've seen other characters; certain Master Yis make me want to surrender since they just do too much damage and are hugely fed, and no one can tell me they've never seen a Ryze they have never wanted to reach through the computer and strangle. But the majority of the players who play these characters don't always do well, and everytime I pick up a new champion, I'm usually terrible.