Acies quadrata

[Flavivs Aetivs]

The only troops he saw were probably protectores... nothing more than a placeholder for people earmarked for future office... never saw combat and never wore armor

Just as a side issue, I'd have to disagree with that! The protectores, by the early 4th century, were largely recruited from the centurionate and were probably very experienced soldiers (the equivalent of the primipilares of an earlier era). Several inscription testify to them fighting, and dying, in battle. By Ammianus's day a proportion seem to have been younger men selected from officers' and bureaucrats' families, but Ammianus himself and his comrades fought at Amida and elsewhere. By Vegetius's day there might also have been a number of young barbarian nobles, like the Burgundian Hariulfus who died at Trier. But we still be wary of casting the protectores into the 'imitation soldiers' bracket... ;-)

More pertinently to this debate, however, they almost certainly didn't perform drill or fight in formation!

You are right in that regard - originally they were soldiers, but by Vegetius' time it was a launching point for the careers of the men like Avitus, Aetius, and barbarians like Hariulfus.