Not true. Most of my TTT gameplay has been spent in vanilla knife servers, meaning either instakill or not depending on the release version. I'm not going to argue with you about the merits of the current knife, as it has been done so many times before, but I personally hate stumbling into a "vanilla" server only to find that the only way it can be construed as "vanilla" is in its adherence to the general expectations, meaning modded knife among possibly other overdone things (large max player count, haste mode off, etc). When I want to visit a vanilla server, I want it to be vanilla in the absolute sense, not the relative.
What this guy said. And if you can't get a kill with a vanilla knife, then you're clearly playing the terrorist role all wrong.