depend on what type of 'sword' referring.
hell, the reason great sword saw its decline in the battlefield is no more because of the advent of rapier as sidearm to musketeer. while try striking plate armor with sword blade is dumb, there's technique that could be used to deal with armor when you only get a sword on your hand and cant bothe to switch weapon
No doubt there were swords used against plate successfully, they needed a stabbing action to work.
As I understand, 2 handed swords lasted all the way to pike and gun formations, their sheer momentum and force I guess, worked against plate as well as a heavy axe would.
while past 250 meter i would agree that arrow do lose their penetration power significantly, an injury by single arrow is often cause death more than stroke of sword or mace. Often it were caused by simple thing like the struggle to pulling off the arrow tip, and even worse it sometime cause infection if the arrow were latched with dirt first (which sometime archer ussually do before the battle). Oh and my favorite, curae poisoned arrow!
A single arrow which penetrates is comparable to a single blow of a melee weapon, but the chance of being repeatedly penetrated by an arrow is unlikely.
Arrows mostly cause their damage from either bleeding, or the lucky penetration to a major organ (VERY unlikely if it goes through even a bog-standard gamberson and chain armour, yet alone plate)
Infection is a nasty thing which caused many deaths by arrows, but its way too slow to be reliable in a fight.
A dude with 5 arrows partially stuck into him can potentially still fight and charge ahead, a dude with 5 mace blows is probably wondering where some of his bones went.
Poison arrows/Dirty arrows were used, but I don't really see any statistics that it was particularly common, normally dirty weapons were frowned upon in medieval warfare (like bloody swords and such).