Gosh, man, it is no matter of being smart but a matter of amount of work. Is it possible to build a whole city all alone? without tools? Try it yourself.
I didn't say it I want to do it without tools. I understand your point, but is not exactly the same. You build a city and your're done with the tools, but a game engine is the base of a game, its foundation; once you finish with it, you're not done with the tools.
Gosh II : "You build a city" ? try to build a city even if you have al vehicles and materials - you probably will do not build one house
A game engine is not just a tool for a game, that is what I'm trying to say and that's how I see it. But I guess you've just wanted to show me how hard and time consuming it is, so I understand.
However, if I were to get to the crux of your closing question...
Is it possible for an average guy to learn what it needs to learn in order to create a beautiful game without an existing game engine? A game that could look almost as beautiful as CryEngine/Unigine capabilities? Speaking just in terms of technology, not the art content that contribute to the beauty.
Is it possible with so many resources/knowledge available these days on the internet?
No. It's probably not possible for a way-above-average guy to make something look almost as beautiful as CryEngine/Unigine capabilities WITH an existing game engine. It requires an immense amount of technical know-how, hundreds of thousands of man-hours, and skilled artists.
I'm not saying this to deter you necessarily, but you won't get anything that impressive on your own no matter what you do. However, there's an ocean of space in between Pong and Crysis.
Yes, I know that it's also the art that makes things beautiful. I was strictly speaking from the technical side only, but I think somehow you was referring to that also when you've said that it's not possible, right?
So, if someone wants to just make a 3D game that comes close to the quality of a commercial engine, speaking only from the technical side of things, the programming side and not art or other content, he should try and use a commercial engine?