The fact that there's still a lot of buildings still standing doesn't mean they were built perfect, it just means their construction has the possibility of lasting a 1000 years. For each of those buildings I bet there were 10 more with the exact same building techniques that are no longer standing.
A 1000 years is a lot of time to go without a fire. I think just because of the fire risk wood is simply out of the question. Well unless you can protect the wood against fire like the OP is doing with the steel.
Considering modern times, I think you would have to go one step further and also consider gas explosions and possibly being bombed as well. Just imagine how many 1000+ yr old buildings must have been in Germany before WW2.
There are more old buildings left in Germany than one might first assume. The devastation of WW2 was most concentrated in the major cities, and minor cities and villages often have old centers that survived fully intact. This was a bit surprising at least for me when touring the smaller places.
There's another bias here that available materials were very different 1000 years ago.
Designing with WW2 in mind is preparing for the next conflict based on the last one. Climate change will have implications, which tend to come out as fire and flooding. This will impact siting.
A 1000 years is a lot of time to go without a fire. I think just because of the fire risk wood is simply out of the question. Well unless you can protect the wood against fire like the OP is doing with the steel.
Considering modern times, I think you would have to go one step further and also consider gas explosions and possibly being bombed as well. Just imagine how many 1000+ yr old buildings must have been in Germany before WW2.