Hypothetically if you had only two states, one with 20 people and the other with 20 million (entirely feasible with the Constitution), would it be useful to given them both 2 Senators each? Would the federal government's laws and actions faithfully represent how the people in the nation actually feel?

This isn't a hypothetical concern. See the laws on marijuana for why "representation for states" isn't ideal. For further evidence, see action on climate change.