It depends on where they fight.
If the fight in a city, it could mean Luffy's death fairly comfortably due the fact humans use a whole lot of metal for all kinds of things.
Also, against those soldiers, Luffy's strongest punch (The Gear3rd punch) was portrayed to be more or less equal to when Kidd just gathers loads of metal into the shape of a fist and performs a move in a similar manner. I don't think their firepower was strong than one another back then.
So its wrong to say "we've seen nothing"
To be fair, we did see scenes of him taking on Pacifista(s) with Law iirc.