It's kind of silly that Tolkien and Lewis are constantly positioned as polar opposites when it comes to worldbuilding. Lewis might just throw a bunch of wildly different stuff together and call it a world, but Tolkien's doing the same thing, too--he's making this huge mishmash of tons of different stories he loves. The only difference is that Tolkien puts in a lot of work to weave these into a cohesive history, rather than giving us a lot of little details and letting us imaginations how they all fit together.
Also, it's silly that people compare Narnia and the Lord of the Rings. They're completely different genres written for different audiences. Of course the series written for literal children isn't going to be as complex as a sprawling epic fantasy for adults. The better comparison would be between Narnia and The Hobbit. Or better, between Narnia and Roverandom. Compare the fun stories written for children based on events from real life.
Maybe the real difference between Tolkien and Lewis is that Lewis stories take an ordinary human and send them to a magical world where they confront a bunch of weird things all at once, while Tolkien stories (all three that I've mentioned) take an ordinary non-human guy and send him on a quest that lets him meet all these weird people one at a time.
