Paid homework projects are far superior. Plagiarism checks can be run on the provided solutions, and a follow-up conversation concerning the project at the interview should easily suss out anyone who had a third party to do it for them.
That approach also has the advantage of actually being a relevant to the position—unlike some generalized intelligence test.
Frankly if people are putting up with the test they have now, Amazon could probably get away with issuing unpaid homework projects, however classless that would be.