Thank you for the correction, I was under the impression that masonry and architecture negated a much higher amount of damage from siege weapons. In this case, then yes, it is pretty negligible.
I tend to get a few things mixed up when playing around with numbers in AOE, so I jumped into the editor to test out a few scenarios and found out some interesting tidbits.
Aginst infantry, you get a slightly different story: champ vs FU barracks (masonry+architecture) deals 10 damage; against a Byzantine barracks, it deals 12 damage. Considering you are usually destroying buildings with more than one unit, that could be significant if you have vils repairing on the other side (7 vils vs 9 vils to prevent the building from slowly dying). But then again, in imperial people aren’t usually repairing building walls (or out of desperation). Plus you’d just be better off building another layer behind your initial walls.
To summarize, under sustained melee unit damage, dark and feudal byzantine buildings are better (longer time to be destroyed, same damage taken so same number of vils to repair: for example, 10 m@a will destroy a generic barracks in 37 secs, a byzantine barracks in 45 seconds, at 1.0 speed).
In castle age, especially in an early knight rush (usually players would not have researched masonry at that time), Byzantines will get the upper hand, because the increased building HP gives the defending player more time to react (ie send more vils, send military). Researching masonry is mostly done later in the castle age/early imp, and at that time you’d be fighting off siege attacking your castles and stone walls, not repairing barracks and houses.
Under sustained siege weapon fire, byzantines are basically the same as other civ, with their additionnal building HP giving them a longer time to fall (when thinking of castles under treb fire).
All in all, the armor coming from masonry and architecture doesn’t do much in the late game when looking at sustaining and repairing, and the byzantines surely don’t miss it.
So come to think of it, a repair bonus to the byzantines wouldn’t be a crutch, it would be a pretty large buff to their ability to buy more time under pressure.
To add in another element, it does takes longer to repair their stuff (to full HP), but they do get a good HP per stone spent ratio (12.5 HP per stone), so that’s another benefit they have, higher than the incas (11.5 HP per stone), and only beaten by the franks (14.4 HP per stone) when looking at castles.
And on top of that you save up on masonry and architecture.
A pretty good bonus overall, that fits their theme perfectly.