Your first point is completely wrong because we're talking about spears and not lances. Also, we dont need spears in SP? Spearmen were the most common soldiers in human history.Spears are supoptimal (not useless) in Warband SP, because you don't need them there. MP is a different story. As opposed to bots that don't use cavalry very effectively, humans do. Without a spear or ranged weapon it's really difficult to counter a human player that plays cav competently.
One handed spear with shield does not exist in a vacuum. You use this to assist team mates and to counter cav while under archer/xbow fire. If you're not under fire, you switch to 2H spear (and decent players typically block well enough for the lack of a shield to not be an issue).
People just play naked in Warband for lulz, if there are good archers on enemy team it's clearly suboptimal to risk additional one hit deaths. If they 'destroy everyone' it's because everyone else on the server is bad, in comparison.
your second point doesnt make sense too In MP a lot of times me and my buds went with spear and shield and played together and it didnt work, the best infantry fighting type does not work. Theres no point for 2h spears if you can get Polearms
third point completely wrong too they dont go naked for lulz, they run like f*ktards and beause damage is almost completely random in Warband they can sometimes survive 4 hits. While if you get full blakc armor you can even get oneshoted.... Happens all the time