One of the main reasons the spear a usually supperior weapon wasnt used by nobles was the fact that it was also a team weapon. A battle was a competition of sorts for nobles, teamwork existed but fighting as a cohesive unit wouldnt work when you out to best the man beside you. So most ditched the spear and went for the sword, mace etc. The sword was also favored for chivalry reasons, it represented a cross. You will notice though that as the medieval period went on, the sword steadily became elongated and slowly became to be like a spear though. By the time of the repier you can no longer slash with it, it is purely for thrusting like a spear.
As for the gladius, thats something of a different beast. It wasnt just the gladius though, it was used with a large skutum the two complimented each other well. It allowed for more flexibility then the pike and spear but the close range weapon also forced it's user to be in a disciplined formation. Imo though the gladius was truly one of the better weapons created throughout history.
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