I was reading a travelogue written by a Russian monk (? not sure, either a monk or a wealthy boyar predisposed to the Holy stuff) who was visiting Constantinople sometimes in the early 1300s, so a century after the whole tragedy, and he was still describing how destroyed the city looked because of the Franks and what big of a tragedy that was.
What I find most interesting is the Romans were unbeatable in battle, even the Byzantines. However, maintaining a large military presence was expensive and politically difficult to manage. So they used annual mercenaries from the north for the usual frontier squabbles, and the main army did the heavy lifting. It fell apart when there was a major conflict, and didn't help that the army held the city hostage demanding more money. So everyone was corrupt it would seem. Also there were the persistence of rumors of knights that may have kept most of the treasure for themselves and headed off to Cyprus. The Knights Templar were insanely wealthy given the times and cost of resources to mount expeditions.
https://en.wikipedia.org/wiki/Massacre_of_the_Latins
https://thetemplarknight.com/2021/12/13/cyprus-knights-templ...
They were, though? Adrianople, Yarmoud, Manzikert, Myriokephalon etc. it's just that the empire was extremely resilient and was generally able to recover from disasters which would have led to the collapse of most other states.
https://kalebatlantaprime.medium.com/the-great-schism-was-in...
e.g. There is currently a schism between the Orthodox Church and the Russian Orthodox Church which technically is not that different. Does that mean that the Russian Church is no longer Orthodox?