I think an honest conversation like you said is good and a working relationship will be helpful.
PS: Maybe what you can "teach" your employees is not so important, but some other things do, like opportunities，other brilliant colleagues that you can offer. They can figure out how to be better themselves :)
A good company will consider about growing with its employees. So maybe managers also need to think about what if the candidate says"what will be my biggest risk in work for you, and what steps will you take to mitigate it?"
I agree with you. Although Material is great, it doesn't mean the quality of Android apps will be improved quickly. Maybe google need to try harder to expand the influence of his guideline.