I don't know what chart you use, but here's the AD&D chart.
At worst, a longsword is 5 behind the best weapon (lance) and a two handed sword is outright better than just about anything at any armor class. And, other than a few polearms, which are almost never magical anyway, a longsword is still the out and out best choice. I notice you talk about full plate, which means I'm using the Unearthed Arcana. I'll take double specs in longsword vs pretty much any other weapon choice out there.
I mean, you mention using a spear (-2 vs full plate) which is exactly the same as a longsword. In a couple of cases, a mace might be better, but, overall? Not so much. And, of course, the fact that almost all magic weapons and certainly the best ones are swords, it's not really a shock that everyone uses swords.