The new Basecamp doesn't have less features than Basecamp Classic. It has different features. The new Basecamp has dozens and dozens of features that Classic doesn't have. All together, I can make a very strong case that the new Basecamp offers significantly more functionality than Classic. And it's simpler, too.

Comparing side by side isn't the end goal. The goal is which product fits you best. If you love Classic, you can stay with Classic. If you prefer the feature/UI/ideas mix of the new Basecamp, come on over.