The Abandonment of the Gladius for the Spatha - Why?

[Tarbicus]

So when you have two men in the same height range, isn't the man with the gladius left at a disadvantage ?

If you adopt a low stance you can reach your opponent with a shorter weapon even though his is longer. If the legionaries crouched behind their scuta aiming for lower targets (i.e stomach, armpit) this would've allowed them to gain a geometrical advantage despite the sword length difference.

This Connolly theory is, in my opinion, quite weak and, quite franckly, banal.

Is it therefore any coincidence that the shorter the gladius became the longer the helmet's neckguard grew as well? Once the spatha became more common - a weapon with longer reach - neckguards shortened again and provided less cover for the shoulders and upper back. Doesn't that support Connolly's theory of the neckguard's evolution and crouching stance, in which there seems to be a relationship between sword and helmet size?