Some kids do homework for practice and to figure out what they need to work on. They learn from their mistakes. Then they are prepared for tests.
Kids who look up every homework answer to get 100% may not realize where they have gaps until they have to take a test.
The first kid isn’t a slacker. The second kid is diligent but possibly missing a learning opportunity.
Of course, we don’t know about the kid that you refer to nor do you. Just focus on yourself. If you think his study skills may be more effective than yours, ask him for tips rather than seeing him as a rival.