With all due respect, I would suggest you open up your aperture a bit with regard to "factually relevant" considerations.

Yes, steel and aluminum pre-date composites as does titanium and magnesium. However, while there are examples of composite frame failures out there -- many of them celebrated by those who are overly fond of steel -- there are very few examples of composite tandem frame failures and long-term fatigue was not the issue. The latter is also true of most modern steel and aluminum tandem frames where the failures tend to be rooted in material flaws or process escapes in manufacturing / welding.

What's probably more useful information is how reliable composite tandem frames have proven to be by the people who actually ride them... and in particular who ride them a lot. In this regard, there are many Calfee tandems with 10's of thousands of trouble-free miles on the road; ours is best described as having moderate use as it approaches 20,000 miles; about 4,000 miles of use a year. There are other teams whom we know who log closer to 8 - 10,000 miles a year on their Calfee tandems, including one of the older Calfee Tetra Tetra models from early 2000 and newer Dragonfly models that are used for weekly brevets and endurance events.

In practice, these well-made composite frames have had no reliability or durability issues. Those who know a thing or two about composites will also tell you that long term fatigue life will also be a non-issue.

So, while it is a fact that steel, aluminum, & titanium tandems have a great track record for reliability, there are examples of frame failures that suggest they are prone to material and process escapes with a very low frequency of occurrence. The steel and aluminum tandem frames that spend 99% of their lives sitting unused in garages and basements and get sold with less than 1,000 miles really doesn't add to the body of knowledge of how reliable or durable they are. But we do know there are examples of very high-mileage steel, aluminum AND composite tandem frames that suggest they are all excellent materials. While Paketa's early magnesium V2 tandems had some material and process escapes, those problems appear to have been addressed and the frames that are seeing very heavy-duty use. In fact, some of the strongest tandem teams are now winning national-level events on Calfees and Paketa tandems.... which I would argue is a very strong testament to the strength and predicted reliability of those materials to hold up under some of the most demanding use.

Just some food for thought, as there are various different ways to measure "material experience" and I think most of us "get that".