Although the 1 second silence might have seemed over-powered to some people, it really wasn't. That silence was one of the only things that kept Talon alive. You went and launched your combo, it wasn't a sure kill. With Talon you still had to time your attack. If you didnt time it correcctly, then after the silence ended almost any mage could take out a good bulk of your hp. And I'm not even gonna mention how most mages just poke you down, while you just have w which doesn't really do that much damage early levels and is easy to avoid if you know how to play a bit. Now Talon's e is completely useless, you jump in and get instantly stunned. Or the enemy dashes away. Or Teemo blinds you. Without e, Talons whole combo can be rendered useless against more experienced players. And if you really need to change the silence, at least give him something of equal value in return to make him viable.
"get away scot free with a well-timed ultimate ability."
No, about 90% of the time you need it's damage to take down your opponent. Oh, you got ganked and had to use it to get away? Well, no kill for you then. Even if you use your ult to run you only have 2,5 secons to get away and when someone slows you then well, your dead. Simply get slowed by Akali or maybe charmed by Ahri, who happens to have a pink ward. Damn dude died again? Oh yeah, I forgot to mention that unless you get kills, you will not be able to do much damage. You need to be fed just to stay on the same level with other assassin who can play it safe. Ever played Talon and tried him against other assassins? Although his burst is good, it takes quite a bot of effort to get his opponent low enough for his combo to work. Take Zed for example, no mana problems and has a great poke. Playing against Zed with Talon can turn out really bad, just because he can infinitely poke you.
Also, take Talon's late game, you have tons of damage, but your hp is too damn low to help you get out of most fights. Ffs, if the opponent has thornmail or just a bit more armor, you dont get a kill. God knows how many times I've died simply because of thornmail.
TL;DR: Talon wasn't really hard to shut down. He wasn't the best assassin in game and just because some unskilled players claimed he was op wasn't a good reason to exchange his e for nothing of worth.