I don't think they had a doubt that the Protheans had a role in their technological advancement, as they discovered Prothean ruins like every other race, which led them to the Mass Effect relay in their system, and then to the Citadel. They never thought they were special and did what other species accomplished without Prothean technology.
Keep in mind, until Javik, nobody knew what Protheans looked like and the Prothean grooming you mentioned was thought of as their goddess tens of thousands of years ago. When something has been a part of your culture and religion that long, you tend to accept it, especially since their government mist have known since they kept it such a tight secret and prevented researxh on their religious artifacts.
It's kind of like how we all laugh at the ancient astronaut theory as ridiculous nobsesne only to find out that it's totally true when they find a UFO in the Great Pyramid.