Ranger VS Thief feels like a mismatch, Thief mechanics easily outmatch straight forward Ranger play. This guide shows some of the things the Hybrid Beastmaster can do to overcome this.
IMPORTANT: This build is not designed to counter thieves specifically. While it does have the ability to kill thieves in many situations, it takes a lot of work in order to pull off. This guide aims to demonstrate how it is done. I recommend a condition based bunker/trapper if you just want to defeat D/D thieves specifically.