I genuinely don't understand why Roman > Norman should be considered an odd outlier?
If it was the only path for Rome, then I understand, but I really don't see any reason to believe it will be.
If it's just one of several paths for Rome, what is odd about it? Think backwards from the Modern Age. I prefer to speak about Britain because I know more about it, can anyone tell me what is odd about representing Britain with Rome > Norman > Britain? Sure, there are other ways you could do it, but this is completely fine, there is nothing odd about it as far as I can see.
Let's work back.
Great Britain -> England, Scotland.
Scotland -> Earlier forms of Scotland, Picts, eventually Celts, I guess? I hope I'm not missing anything major here, I'm not a history expert.
England -> Anglo-Saxons, Normans.
Anglo-Saxons - Celts, Saxons. Probably can't go further than that.
Normans -> Norse, Franks.
Franks -> Gauls, Romans.
(pre-post edit: wait, the Bretons should probably be somewhere in there too... this is where my history knowledge is just lacking - are they an Anglo-Saxon precursor?)
I guess that's how far back you can go. Sticking to the three ages (meaning some omissions compared to above), that would leave the theoretically 'valid' routes of ending at Great Britain as:
Celts -> Scots -> Great Britain. Note: you could argue the English are sufficiently dominant in Great Britain that this doesn't fit, but we'll be tolerant here.
Celts -> Anglo-Saxons -> English -> Great Britain, with any of these other than Anglo-Saxons being a possible omission to get to a three-step process.
Saxons -> Anglo-Saxons -> English/Great Britain, depending on which one works better.
Norse -> Normans -> English/Great Britain.
Franks -> Normans -> English/Great Britain.
Gauls -> Normans -> English/Great Britain.
Romans -> Normans -> English/Great Britain.
So yeah, there's only one way to get from Romans to Great Britain, out of at least five Antiquity sources that can get there overall (six if we count the Franks). Similarly, the Franks can go into France or Germany (through the HRE), giving Rome more paths, plus Rome could perhaps go into Castille or something and then Spain or Portugal, obviously there's the Byzantine Empire which leads into modern Greece and perhaps Russia, plus geographically the Ottoman Empire, there's the Papal States or Italic city-states ending at Italy, and I'm sure there's a bunch more options.
Rome -> Normans -> English is a valid path if you look back from England to where things began. That doesn't mean Rome
has to develop in that way, nor that England
has to originate from Rome. Just that they're possibilities.