1) A stupid and silly comparison because in deadliest warrior weapons are often shown as weaker than they are, i.e. a crank based crossbow failing to go past lamellar armour in one of their tests.
Way to miss the point, dude. Specifically the point that in Deadliest Warrior and other such programs they use cheap butted mail.
1a) People had much worse steel then than now, with far worse methods of purification and such and it would often be too brittle or soft, irregularly shaped, much worse maintained and weathered, etc.
Historical steel is not automatically crap because it's old. Historical steel was of fairly high quality, especially by the renaissance, and while we do HAVE better steel today, we don't usually USE better steel. Even the linked video's mail was made with steel worse than historical steel, because the guy making it is an idiot.
2) If that were true than fencing manuals and schools would not teach one to go for a slashing movement for the armpits that are typically protected with mail. Unless of course you are of the meme "European swords kill people with blunt impact" school of thought.
Except they don't, they tell you to grab your sword by the blade and thrust with it. Alternately, it tells you to reverse your weapon and strike with the guard and pommel, but not with a zweihander. Swords are also terrible against armour just in general, which is why they were, with very few exceptions, sidearms. The zweihander was a primary weapon, but it was also a specialty weapon for defeating pike formations, as it was capable of knocking multiple polearms aside to the soldier could get past their points. It also only worked because the soldiers wearing them had plate armour and you can't stab through plate.
3) Yeah and I can post a video of a man using grorious nippon still slicing through plate armour, videos mean shit.
Oh yes, surely people actually trying things and them not working is less evidence than your completely unbacked word.
4) Perhaps not renaissance era cuirasses and such which were much thick and designed to take on firearms, but more traditionally medieval ones you most certainly could. Thus weapons like the tuc were formed. "...As armour improved, so did the methods of attacking the armour ... long tapered swords could also be used as a lance once the lance was splintered..." lances and many polearms being notorious for being able to give plate the old stab.
Except that's not true. The tuck was designed for half-swording, it's an unsharpened, puncturing blade and it was used to thrust between plates, as it STILL couldn't penetrate them. Polearms can also be used this way, but the weightier ones were just used to bludgeon the target. As for lances, those are cavalry weapons. While I don't doubt that in some instances a lance might penetrate lighter plate, that's because it was being used from horseback and has an immense amount of power behind it, and even then it's likely the lance shaft will snap.
Further, all full plate was made to resist firearms, firearms predate full plate. It also isn't that hard to resist them.
Also not wholly true, many soldiers were found without daggers and those that did often brought knives along to be tools, weapons as a last resort and not really brought for that purpose.
I have never found a single source that ever mentioned soldiers without daggers. Not only are they invaluable tools, but grappling was common and daggers outperform other weapons while grappling.