A 19th century rectifier might have filtered whiskey that had some age on it if it hadn't aged very well, to render it more neutral and more suitable for blending. But, yes, it's unlikely that a well-aged whiskey would have been filtered in those days. Just trying to make the point that filtering through charcoal or bone dust has a long history in the industry. It wasn't invented in Lincoln County, Tennessee.
In this case, Diageo felt they had to Dickelize it, so what else could they do? Doing it to new make and then letting it age for five or more years wasn't an option. This way they were able to make something that tastes different from the many other LDI ryes, and a bit milder and smoother, which is also consistent with the Dickel brand. It's a different taste and fair to say it's a funky taste, so it will be interesting to see how people respond to it on taste alone. Whether of not it suits the Dickel brand with be another question.