Two people in a sword fight spend most of the fight about 10' apart - the distance of one step plus an outstretched arm with a sword in it. They only move in to make a blow.
Standing any closer than that is suicide, as you won't have time to parry an incoming blow (and will be forced to try to dodge, likely throwing yourself off balance and getting killed by the continuation of the attack). I talked yesterday about how important *not dodging* is.
"But on the other hand, are we assuming that combatants are too stupid to try to get inside an opponent's reach? Too stupid to knock the spear aside with their shield? It balances out."
It would seem so, but it doesn't, and here's why.
For the person with the longer reach, it's easy to maintain a longer distance. Any time the opponent gets close, you circle away from them (i.e. step sideways and back). At no point is the long-reach person threatened in this series of actions - they are still too far away to be hit.
Additionally, at any point, the person with the reach advantage can simply step forward and attempt a blow in relative safety- they can strike while they are still out of reach of their opponent's weapon.
However, for the person with the shorter reach, in order to attempt a blow, they have to achieve a tactical advantage which will let them simultaneously catch the other person off balance enough that they can't circle away, control the longer weapon as they close (so they don't die), *and only then* can they attempt a blow. Much, much more difficult.
It's certainly not impossible, but hopefully that illustrates why it doesn't "balance out".
This is also a good argument for buffing spears back up to their full length, by the way.