That tightly protected formation is essentially a tank, which would allow armies to amble around the battlefield spear-stabbing everyone, resisting their natural urge for badass, glistening-pecs warfare. Most every successful pre-firearm warrior culture organized special formations like that to whip out against their less strategically minded opponents. Even Vikings, the poster boys of undisciplined berserker rage, often fought in basic shield-wall formations.
As for the whole "break from formation to engage in slow-mo melee combat" thing, it just didn't happen if the warriors knew what they were doing. The thing about fighting shoulder to shoulder in close formation and close enough to the enemy to smell their (lack of) deodorant is that you don't have much room to dance around swinging a sword. As such, especially during the classical era of Greece and Rome, battles between hoplites or legions mostly consisted of which side was better at holding their line and pushing the other side back.
Basically, a slightly less violent version of Red Rover.
In other words, it was tedious as shit, both to watch and participate in. You can see the irony here; the method depends on the other side wanting the same thing movie audiences want now -- acrobatic, one-on-one combat to prove who is the better man. The armies who succumbed to that temptation got their asses kicked.