That's a good point: execution is essential but- using your example of Super Mario Bros- the amount of creativity and original ideas in that game was incredible. Especially for 1985 or whenever.
On the other hand, there are examples of games that use another game's concept and just make it better. Doom with Wolfenstein springs to mind. So, if someone's struggling with ideas then building on existing ones might be a good approach. Or maybe combine ideas to create something original- Fortnite is more or less PUBG mixed with Minecraft and Overwatch-style graphics.