Yup they do. Its hard to make them OP tho. They cant really ever get to ur lvl but im sure you get the idea.

Companions are actually decent, especialy Jocelyn, Lethaldiran, and Alistair. All start over 30+ levels with high proficiencies and decent(Lethaldiran OP) equipment. Getting them to a higher level or proficiency is hard as frick though. At the end of each battle, you can see the kills section at the bottom where casualties are showed.