And the reason they couldn't scratch them with magic was because the scales were too hard, as the person carrying one of the best sword in the series is telling you. Even if you take away the magic from Kagura's sword, it's still a sword. It still cannot scratch the dragons.It does because they are resistant to magic because everyone through magic at them and it didn't work. Physical weapons do work as the soldiers of the past have proven. Kagura's sword is for magic usage. That does mean Belserion is unreliable, he should have, he did not think that such a thing was possible so he would have thought of what might happen, he was suppose to protect Irene anyway. he is just being hyperbolic. Yet it did happen, Belserion was just an idiot for letting his pride get the better of him. Non of them showed weapons, even if we take the anime into consideration, none of them had weapons nor uniforms to match. DS enchanted weapons concept did not even exist back them. DS are weakened back then so their attacks would not be as effective, even then Dragons did not kill anyone then
Belserion, the Dragon of Wisdom = An idiot? Not being able to predict the side effects of dragon slaying magic has absolutely nothing to do with assessing the power it takes to beat a dragons. Belserion wasn't speaking out of pride. He was speaking out of concern to protect Irene. If he thought that humans could hurt dragons, he would have let them join the fight.
Like I said, all of the soldiers going into battle would have been dragon slayers. How do you know that not a single one carried weapons? Some would have been former soldiers, and may have opted to carry weapons out of habit. Some may have ditched them. Also, how do you know enchanting dragon slaying magic into weapons wasn't a concept? And no, Irene going "wha-?" isn't proof that enchanting DS magic wasn't a concept. Irene could have simply been surprised that Wendy was able to pull it off because you know....Wendy was unconscious up until a few moments ago.
It's not just during the GMG. Current Gajeel would still struggle to do much against an average dragon like Animus. Base Natsu can block Gajeel's secret art, which is when he turns his arms into a giant sword. Animus is physically tougher than base Natsu (his horn impaled Natsu's torso), and would likely outright defeat Gajeel. This idea that a regular foot-soldier is taking down a dragon with a regular spear is insane.

