You're so close to getting the issue here. Yes, the issue is that these changes were the result of conquest/subjugation, not the result of some nebulous crisis.
The “nebulous crisis” are conquest/subjugation (barbarians, revolutions)…as are
most of those switches IRL history.
What civ does is say, “what if”
The key point is the player can interpret the what if how they want.
It can be….
What if Rome->Norman was more like Rome->Byzantium
an internal development…adopting “Norman” practices helped them bounce back from the crisis …In my game maybe that’s how it worked.
or it can be
What if rebellious Asians sided with barbarians, destroyed Rome and founded Byzantium on the ashes. (if I want to say that’s what happened)
As far as I'm aware the term historical and regional paths are one in the same, correct? They are just alternate names for branching paths, whether Egypt goes into Songhai or the Abbasids naturally.
No I think historical path(s) are the most restrictive of the regional paths…
ie
Egypt->Songhai is a regional path
Egypt->Abbasids is the historical one
For some civs the historical path will be sort of weak(only regional)…Songhai was only shown to unlock Buganda…. but presumably that’s because its the best Age3 civ for Songhai now… but DLC could bring better contenders.
And I do imagine Some civs will have multiple “historic” paths….like Rome might unlock Normans, Byzantines, Abbasids…but only Normans and Byzantines are counted as “Historical”