I think it could be reasonable to have system where the House represents the people (making proportional representation necessary) while the Senate represents the states. As long as the role of the Senate is sufficiently limited and not the core of the legislative process, that could be very reasonable. But it's vital that the people are more important than the states.
For example, the House could decide on the laws, with the Senate only deciding whether this is an issue that belongs on the federal level at all. And maybe double checking whether the law is constitutional and in line with existing treaties.
If they do the same thing, it makes no sense to have them both.
