nope - use the right material and the lifespan will be easily as good as injection moulded :-)
Given the way you can use very thin layers to form an actual flexible matrix that resists tearing in all directions, I suspect you could probably improve on injection moulded hinges.
There are some seriously amazing materials out there in 3d printer land.
Like I said, get your printer, try some of the more exotic filaments and then come back to me.
3d printed stuff can be way better than you seem to think it is :-)