Irving and Eamon two old men that have no weight in that battle in fact they both are defeated pretty quickly than the PC is alone vs Archdemon+ neverending minions.
You mean in gameplay they have no weight in battle.In story Irving is FE pretty, he is archmage and he is powerful enough to at least defeat desire demon on his own.While Eamon isn't that old he is 46 years old (sure, ain't at his peak but still)) and is war veteran.Plus, there is ballista around to help you and as i there are magical/mechanical gadgets in-universe that would help you combat.
I'd be more inclined to believe that it's stronger after it's reforged given that Corypheus apparently reforged it using his own power and that of the Orb. But even if I conceded this point that shouldn't explain why actually drinking the red lyrium doesn't grant Samson as much power or more, and while I've never fought him while he was still wearing the armor I've never heard that the armor made him anywhere near as dangerous as Meredith either... and it should make him at least as dangerous since I think an entire suit of armor should have more lyrium than the sword does. And that's not to get into the fact that he's using the sword in combination with the other source(s).
This could explain Samson not being as physically strong or as agile, but since he's been trained to use red lyrium effectively by the closest thing to an expert on the subject, and just has so much more of it than Meredith, you'd expect his magic to be at least as strong... and it isn't. He uses basically no magic at all apart from the boost to his brawn the armor grants him.
Not necessarily, assuming there was something special about idol and Meredith sword it's potential could have been severely trampled when Merdith "overheated" it leading it to losing most of it's orginal power, so even if Corypheus enhanced it's power he would only enhance material that has a fraction of it's former potential.Samson armor might not have been as potent red lyrium as Meredith sword was.
Samson was drinking red lyrium in order to enhance his strength, but the same doesn't equatate to having a skill.Meredith was in the possession of idol at least 3 years, we don't know how much how much he spend exposed to red lyrium.Not to mention that active KC would have much more control over her abilities than a Junkie than spend 7+ off duty.Even if red lyrium boosted his physical strength and with his friend help he was able to utilize red lyrium as an armor doesn't mean he was able to control his abilities as well as Meredith. I also want to mention that Meredith went all out to the point her sword exploded and it turned her into a statue.So assuming he even could go to Meredith power level he didn't.