Most game developers are not this good -- I spent some time in the game industry (coming from a webdev background) and it was important for me to know C++, but I didn't really have much graphics experience and I was still really useful. Gameplay and UI code end up being a huge part of what goes into games, and you don't need this level of expertise for that.
That said, graphics engine development is very technically and mathematically advanced, I would say much more so than the web stack.
Yeah, I see how a lot of the skill will apply in both fields, however they feel a universe apart (at least for me). I remember trying to do a pretty simple game (think space invaders clone) in Java and if I'm honest - I struggled (a lot). Now when it comes to the web (both frond-end and back-end) I'm flying. Having said all of that, It might be just that I'm a shitty programmer.
That said, graphics engine development is very technically and mathematically advanced, I would say much more so than the web stack.