I really think that professionals wouldn't call it game programming unless I make my own engine starting from OpenGL
You could make a video game any way you want to, and as long as that method allows you to create your dream end product it doesn't matter how you got there. Plenty of professional and semi-professional studios use unity. Unless you want to take it up as a project for fun, you should never "need" to make your own engine. The people at OpenGL already did that for us.
Yes, this is misleading. People use middlewares, that's why there's Unity, CryEngine, Unreal, Ogre 3D, and all that so you don't have to always start from scratch, even among pros.
It takes time to master multiple skills. To make a nerdy analogy, a fighter-mage combo requires more time to level up than a straight-up fighter or mage.