That was part of my history class in university. There’s even a Youtube series on the Fall of Rome, I think it’s 8 episodes and they were correct. The Roman Army was so big in order to fill the ranks during the last century or so, they promised barbarians citizenship and they got backstabbed. They were NOT loyal to the empire and I doubt a good number of these clowns are either.
Accepting a few percent who join for reasons ideologically aligned with the nation and are integrated with solid soldiers is a whole lot different from farming out the majority of the military.