The two have their fair share of challenges. I don't consider any of them to be superior to the other. Because, web development is 90% programming. Only that it is web programming as opposed to mainstream programming. The amount of effort you will use to master programming is closely similar to the amount of effort you will use to perfect your web development skills.Which one is harder in your opinion?
In my opinion Web development is harder.
That is because you (mostly) need to be able to do computer programming to do web development and you have additional requirements like knowing how your environment works. how database works, how to deal with security and how to design user experience. Not to mention good aesthetics.
Now if you ask if web development or game development is easier, than web development is easier.
Basically computer programming is used everywhere in IT in one form or another. What makes it harder or easier are all additional dependencies you need to deal with. Like mathematics and algorithmic with game programming.
At the same time even if web development has quite well defined goal, it is still very broad subject. There can be very difficult web development (like Photoshop inside a browser) which will be much harder than most of standard stuff you will ever do. And there can be way easier like static sites which are elementary school projects in this days.