I think there's a lot of variation that goes into shocks that all will impact the lifespan. So I don't think you could necessarily say that one design lasts longer than another, but for sure some shock models are more durable than others. And that even applies within different lines of shocks from the same manufacturer.

Typically the parts that wear out most on monotube shocks are the bushings. Spherical bushings simply don't last very long. Maybe 2-4 years in most cases of mixed use. Rubber bushings last a lot longer. For a non-race truck, I prefer rubber bushings any day of the week. But you generally don't find rubber bushings on higher end shocks. They are cheap and easy to replace generally, so it's usually not a huge issue. But it can be a PITA sometimes if you don't do a good job of keeping the misalignments anti-seize coated.

The next most failure prone spot is the hoses and fittings. Again this is a spot where a more basic OEM style shock will last longer. Remote reservoir shocks add a lot more parts including a bunch of hose fittings that are also prone to failure moreso than a simple enclosed shock.

On the flip side of this comparison is heat. With OEM or similar twin tube shocks you can fairly quickly overheat them if you go long distances on washboard roads. I could probably overheat and blow the seals out of a set of OEM shocks in a single day. How durable is that? Larger twin tube shocks could often last as long or longer than monotube shocks in a lot of scenarios. It probably just depends on how they're build and how hard you push them.

The other considerations are how hard and how rust-proof the shock shaft is. Pitting and rust will cause them to wear the seals out quickly and lead to shock failures. Fox factory series uses the hardest shaft I'm aware of in any off the shelf shock for the 4Runner. They're significantly harder than the shaft in a King 2.5 shock. Does that matter? It just depends on how often you are in situations where gravel and rocks are going to pit the shafts. I think most mono-tube higher end shocks use at least double wiper seal sets. Lower cost ones like 5100's use a single wiper set. So there's a redundancy built in to the higher end stuff.

Outside of that - it's really unlikely to ever break a shim or other internal part. It can happen. But it's rare. The most common failures are the bushings, hoses, or wiper seals. If I were choosing a shock set to go a million miles and I couldn't replace or repair along the way - I'd buy the best twin tube shock I could find that has the body down and shaft up and I'd do my best to make sure the shaft was protected well from flying rocks and gravel.