Great questions. I would say from a pure physics perspective - no, they do less work. Due to mechanical constraints, they are somewhat limited in how much mileage they can do. So yes, I would argue it can help to cross-train. Depends on the run event as well.

So, for world-class athletes does it matter more how specific they can be with HOW they accumulate their work within their (anyway very high) maximal sustainable total workload (e.g, kJ per week)?

More on that soon 🙃
End/

Elite athletes have a much higher power/speed output ➡️ Their hours of training involves a much higher energy turnover (in kJ) compared to e.g. lower tier athletes.
A higher training volume for them - It’s not just hours, it‘s WORK!
3/

Volume is often a good distinguisher between world-class and lower tier athletes.

Figure from Sandbakk et al. 2016 comparing world-class and national class XC skiers.

The question is, is there still a direct correlation between volume and performance in high-level homogenous groups?
2/