So what you're saying is, Assassins shouldn't be able to assassinate. The definition of assassinate is, "To murder in a surprise attack". Getting into a fight with something is not murdering it in a surprise attack, it's dueling it. As Talon, back in Season 5, I was able to ult speed boost assassinate single targets in under a second. Why? Because they were alone and I could. In a teamfight, flank and eliminate. Know how they caught me out? Either body blocking my clicks, or finding and ccing me before I could murder someone. That's how you beat an assassin.
Fast forward, this season. Talon now requires longer to burst. Too long, really. To the point that I end up in a duel with people to see if I can burst them before they 3 auto attack me. That's not healthy. It eliminates the entire purpose of being an assassin.
And to respond in a more direct manner, catching you out and bursting you before you can do anything IS working for a kill. And it's definitely not free. I have cooldowns, and I still have to escape. If I ran straight at you in full view, how do I kill you doing that? I either don't, or I get killed at the same time.