Although it's still an opinion, but I'd put the things that way: game engine is the game itself. I'd also say (although this can be very criticized) as example: Half-Life is a game which has game engine. Counter-strike uses Half-Life as game engine. That way, if you reuse a game engine, you're just making another mod (usually critics goes after this ). Once finished you just can't change its graphics core. All game development begins with its design, just like any application. You'd know that you'd avoid changes in the design because it'll lead to changes in the whole system so that when you choose graphics engine you'll be using it for the whole project.
PowerDraw and other similar components are "game development helpers", that is they accelerate your game development and allow you to make games more efficiently.
There're people that work only on "game engine" (which is nothing more but a functional parts of some sort of game), hoping to use it further in the future. There's a code reutilization indeed, but when you develop a game, you'd most probably end up making its own engine. Conclusion: I'd suggest you make a design first, then pick the necessary tools (which includes a graphics library) and then get to work on the game engine in order to make a complete game.

- Lifepower