The armor has very good coverage (better than modern military armor except bomb suits), but personally I wouldn't call armor "full body" unless it also covers the arms, legs, and at least some of the tops of the feet, plus of course a more complete full head helmet.
Leg and foot armor was often times unnecessary in bronze age combat.
Spears are meant to keep the enemy at a distance. Aiming for the foot would require some reaching, putting you in significant danger of counter attack. Armies lined up in row and each man covered the man to his right so reaching in battle would be a risky maneuver.
As for protection against arrows only requires a thin layer of armor to deflect, and that armor is best located above the knee since arrows come from above. Alexander’s phalanx did not utilize foot or leg protection except for the most prestigious officers. Their thin shields were wide enough to cover their body, and it was noted that a phalanx with their spears raised, could scatter a volley of arrows along the spear shafts.
Keep in mind all of this equipment needs to be packed and marched long distances, in the summer heat since armies did not campaign in the winter due to challenges with provisioning a sizable armies in wintertime. The wealthy elite could have baggage trains to carry superfluous equipment, but the bulk of any army marched on their own two legs and carried everything they went to war with on their backs.
The basic concept of Phalanxes date back to 2500BC at least. Greek hoplites might be more recent, but it’s a surety that the basics were in place long before that.
Full body armour (probably expensive), along with swords suggest that’s this was probably the armour of someone high ranking, rather than a common soldier.
He talks about the economics of bronze age warriors, how most soldiers were generally expected to bring their own arms and armor which could be costly, and how soldiers would prioritize armoring their heads and torsos before other body parts.
The apparent "impractically" of the armor is one of the very reasons it's being tested. I think the apparent reduction in visibility is probably being exaggerated in some of the pictures that they've chosen to use. In addition, since a lot of the fighting would be with spears, I'd assume there would often be enough distance that the high visor wouldn't obstruct too much relevant vision.
I agree, the camera angle is from below and the spearman seems to be tilting his head. Figure 3 in the paper has a image showing an angle that implies the spearman had decent vision.
It is probably compensated by the shield and the heavier torso armor. Attacks to legs (depending upon height differences) reduces the measure unless the attacker squat and thrust without leaning forward.
Big shields also have similar issues with visibility. They can protect you, but they also cut visibility.
