I certainly agree that Nintendo have not done anything similar to this. But what if Nintendo would make a browser-based Mario game with the same functionality? Would it be fair that they , the original authors, would have to compete with him?

In these situations in general it is best to think about extremes in both ends. At one extreme there is round corners on the phone - requires no effort at all to "research". Not allowing to duplicate such work is absurd to anyone who has common sense. On the other end - drug formulas. Requires many scientists' hours, expensive equipment and years of testing to come to market, but can be very easily taken apart and duplicated once it is done. It is clear that it would be unfair if he who researched this formula needs to compete with all the copycats who may only be investing in drug reverse-engineering and mass production. It's really hard to draw the line imo, more so to make a law that could not be abused somehow.