That is very true. Personally I would use ebony for the Ark. But I suppose a survey of the land should be taken to determine which woods are currently available in the area and, more importantly, which woods came from that area at that time. I would personally love to see the Ark in pristine condition, but unfortunately the facts do not point in that direction.
Can we assume they used the local material? Were they carrying supplies such as oak or ebony? Did others repair the Ark over the time? Can we assume this? Etc. So many variables to consider.
The same should be said with the wood's stability, regardless of which wood or repairs. That was only one condition (my scenario of Tut Conditions), but if the ark is deeper in a mountain resulting in cooler conditions we have more variables to consider. Climate changes with the region, but I will not assume a region and stay with it left in situ in a cave/carved mountain. Imagine the Ark placed deeper underground than Tut's tomb. We lose the heat and dryness that preserves (e.g. mummies, etc). That in itself is bad, but now lets imagine for a period as short as 100 years, once a day, or even a week, an elite enters the mountain cave to worship with the Ark. The moisture from his breath only adds to the problem.
But since location, conditions, repairs, history, etc are all unknown we can only speculate. That actually sounds like a good pet project I might start. Take each region the Ark is theorized/rumored/or said to be in and put them through various scenarios with the variables: Wood, Repairs (yes/no), Dimensions of the Lid/Angles (for variables in weight of Gold), Climate, Room (cave/cavern, Church, or other). Factor in geological conditions at the time the Ark was "lost" for the climate since that time and don't forget eruptions or earthquakes for the regions. That should provide a better idea of the condition of the Ark in each local.
Of course once the project chart is finished, believers of certain locals that are not probable will just say: Power of God kept it in perfect condition!