@Ulthair - I think it's better to think of that sword as an extra life potion in the shape of a sword. Extra life potion that also grants you a surge of mountain-rending power.
I think it was a more reasonable weapon in the WN - it was just a sword that granted a great amount of power by tapping the dragon veins in the ground, but had a tendency to cause people to self-destruct with that much power. And the MC did all the tactics of getting himself "killed" on the fly, instead of relying on the sword.
So news of his older brother and father defending the border reached the capital despite happening quite recently, but news of even one of the many times he has killed demons hasn't reached the rural areas? I mean sure rural areas are slow for news but c'mon now. You would think bare minimum the massive siege deal would've had them send out for reinforcements to defend the capital.
@Lioslin My Guess? There is more traffic and communications between Border Stations and larger cities than smaller villages who maybe see a merchant a week at best, if not a month. And even then if someone told me "Oh yeah, Demons are back and some kid is murdering them left and right" I would probably think he's drunk.
@Lioslin : Keep in mind this brother is an extremely arrogant idiot. There was 3 years between CH 2 and CH 3, and he has no excuse for not knowing how strong Mathias is from those 3 years (though I suspect his pride and brain washing about the superiority of his 1st mark would not let him see reality). There is a reason Mathias uses him as a measure of incompetence.
News could have reached their family, which I feel is very likely since they would have wanted to ask Pops what the F*@& he did raising Mathias to make him so superior, and he would not have listened or accepted it. He is not smart enough to see beyond their marks and the ranking he was raised to believe.
EDIT : I just when back through the WN and
When Matthias talks with his Dad they were aware of Mathias's exploits, to some level (there are inaccuracies mixed in). Pops even says Idiot Bro was basically his only real problem until the present circumstances. Also There was a ranking of how effective people were at taking down the wood dolls and Pops ranked 1st with 50, Oldest Bro 2nd with 32, Idiot bro was 5th with 4. Mathias had trouble accepting that he was not in the bottom half, but keep in mind only oldest bro knows chantless casting of those ranked.
@CaTastrophy427 : Not yet, let him a deeper grave for himself . Though Matty is only a disappointment in his obviously idiotic eyes, but is actually valued by everyone else in the family, which idiot bro has no excuse for not knowing.
dragon vein sword is a different one, that was mass produced. Man-eater blade is close to when the WN was axed, so a few arcs off. This sword was spesifically made by him, and I too feel like the WN handled this sword better, that he was so involved with managing the mana that he couldn't even use any detection because he was nothing but a ball over overloading mana himself, etc.
Also, nearly time to reintroduce the biffgel/vivgel unit of messurement for how many you have to sacrifice to kill an enemy! lol.