It's more about linguistic structure than origin of words.

Kannada, Telugu & Malayalam, even pre-dravidan-movement Tamil have lot of borrowed sanskrit vocabulary, but they retain structure of Dravidian languages.

Also most common words used are also Dravidan origin.

For example:

Kannada - Naanu, Tamil - Naan, Telugu - Nenu, Malayalam - Njan

Etc..

Another small thing unique about Dravidian languages is clusivity, there's exclusive 'we' and inclusive 'we'. While modern Kannada, unlike Tamil / Telugu, doesn't retain this feature, some dialects such as Havyaka retain this feature.