If I load up a smith machine for instance, with the effective weight of 405lbs and do incline bench press on it for reps, would you think I wasn't strong?
I'd say you were good at moving a weight through a mechanically-restrained bar path. I'd be more impressed if you could free-press a bar with... I don't know, but less than that.
It's just a matter of what you want to accomplish. If you want to be able to push a weight through a track in a machine, than that's the best way to practice that skill. If you want to really lift heavy things, then lift some heavy things.