Julian II (the Apostate) and his policies

[S SEVERUS]

Okay, now we have some numbers. Something like 54,000 dead Romans in the context of a civil war. The battle of Mursa in and of itself resulted in a larger loss of life, sure. But I take issue with calling it a bigger disaster because the consequences were not as disastrous for the Empire as Adrianople since the enemy were Goths who had invaded and defeated Rome within Roman territory. The Empire could probably cope with Mursa far better since all the Romans would have to do is enroll barbarians into the army to make up for the losses.

Theodosius The Great

So, that's just what Theodosius The Great did after Adrianople. What I wanted to stress is that Adrianople, just as Mursa, Abrittus, ... was not a blow the Roman Empire could not cope with. Like always, losse could be made good.

I don't follow you with you're dynastic principle simply because it makes no sense. In the Roman and Byzantine Empire there was never a long lasting dynasty like you have in the medieval France or England. There were uprisings, usurpers (succesful or not).
Relative peace after the conversion of Constantine? One of his sons was even killed in battle by a brother, Julian took over power, even Theodoius The Great had to deal with a very dangerous uprising and his sons, well yeah, they were pawns in the hands of others.