The OP is right about the Western tech group, but that's only the tip of the iceberg. A proper overhaul should include at least the following:
- Constantinople should start as a size 4 fort (some people would say more but let's not exaggerate)
- Byzantium really should have cores on all the Eastern Roman Empire, with missions for cores on the Western half
- The national traditions and ideas really need an overhaul. I'm thinking something like:
- NTs: Greek Fire: +100% Galley combat ability, Imperial Reach: +5 diplomatic ability, Legacy of Empire: +5 yearly prestige
- NIs:
- Cataphracts: +100% Cavalry combat ability
- SPQR: -5 revolt risk
- Legacy of Plato: -50% idea cost
- Roman conquests: -75% coring cost
- Legions reborn: +150% Infantry combat ability
- Tributary states: +5 diplomatic relations
- Roman concrete: -75% building cost
- Roman discipline: +50% discipline
- Classical Heritage: -50% technology cost
- Garrison towns: +100% colony growth
- Pax Romana: 80% AE reduction
- Imperial Prestige: -75% vassal integration cost
(yes, that's more than eight, but whatever, Byzantium should have more)
- Ambition: Empire Reborn: permanent 100 prestige, 100 legitimacy and +3 stability.
Of course restoring the Roman Empire should switch you to better NIs than those.
Also, Byzantium really should also be the union tag for South Slavic as well, and the restored Empire the union tag for Latin, French, Iberian, and British (I'm being reasonable and not adding German there).
That would be a good start to make Byzantium's starting position a little more realistic, while we wait for a proper DLC.