The definition "destroy a large number of" has been around for centuries. You're contradicting long established usage, while pretending to appeal to it.
I am not contradicting it. From their context it was not possible to tell if they meant the deaths of 1 in 10, a number similar to that, about half of all people, 9 in 10, 99 in 100 etc. I gave the proportions as remembered from the book as that gives a far clearer picture.
Here's the dictionary definition of decimate. The primary definition is "destroy a large number of". This isn't recent - I looked it up in the full OED and it's been around for centuries.
Are you wishing that the current usage of the word (the title you linked to) would stop, and that usage would revert to the older Latin meaning? Unfortunately that's not how language develops.
I am wishing that articles about history are more precise in their usage, since it can be difficult to tell which sense they mean of the word (historical, at the time of the material they are writing about, current meaning applied to back then).
The 1491 book put the death rates at around 1 in 20 surviving - ie 19 out of every 20 people dying from disease etc.