Hi all!
I think that the roman and greek bias against hellenistic kings it's still alive in public opinion.
Greek culture was adopted far beyond the limits of the greek colonisation and of the macedonian conquests. Even western civiliations like ertuscan and Carthage were heavy influenced by it.
Despite often struggels for power it must be noted that both Seleucid and Ptolemeic dinasties survived and no other dinasty toppled them like it happened so often in the Roman Empire. The profesional armies used by them were much better then the persian levies and later Rome will follow the same path.
Political unrest was a normal problem in kingdoms created by a thin foreign elite, with no traditional borders or political institutions.
I don't see why ethnic diversity was considered a problem of the Seleucid Kingdom when all Middle East empires had a similar issue.
The hellenistic world did not collapsed, it was defeated and united by Rome.