Does a 4-pin XLR cable actually contain 4 separate conductors? Alternatives?
Yes.

The 4-pin XLR cable is popular with intercom headset systems. Two pins are used for the mono headphone signal and two pins for the unbalanced microphone signal, the cables will have all four populated for this purpose. However, it's audio and low-power so the conductor thickness (current carrying capacity) is typically smaller than you would need. There are 4-pin power cables, but these, as you note, do not always have all four and when they do sometimes the off-pair is a smaller diameter designed for a control signal (like synchronizing flash systems in photography -- just a low-power sync signal that triggers the high-current load on the other conductor pair).

Some Audio XLR cables contain all three circuits (conductors) through wired and you have an outer braided shielding that is isolated from the three circuits giving you potentially four independent electrical networks if you desired to use it that way. Audio cables can be designed for very high audio powers and low signal losses over long distances and may be sized big enough to carry your 10A DC with sufficiently low voltage loss.

But... as you observed, conductor quality and inclusion varies greatly among manufacturers and product lines. Best to open a sample up and inspect it to be sure.

Check out machine cable assemblies

Industrial/factory automation equipment has similar demands to your application and therefore their standard products will also serve you well enough.

For example, "Brad M12" connector systems are quite popular. But, be careful there is a range of conductors used with this type of connector and not all of them can handle your 10A requirement.