Grumpy, if I were you I'd wait for your new Quark 123 before drawing final conclusions. I could have missed some information in this thread but it's still not clear for me what is the exact situation.
Marduke wrote that the EX10 uses boost only circuit. If I understand correctly, it means that the light behavior depends on the LED Vf, over which Nitecore has completely no control, and on the battery voltage under the load which obviously is also different for different batteries.
If you happen to have a light with a low Vf LED and use a good battery with a low voltage sag under load, I think the light can easily run 15 minutes in direct drive. During that time, the light would run bright and, if not cooled, hot. I mean really hot - I tested an AA direct driven light some time ago and without cooling in the room temperature the light body after 15 minutes reached 66 degrees Celsius. In that temperature you couldn't hold it even for a few seconds. After these 15 minutes there will be only half of the initial battery capacity available for the regulated runtime.
You may also have a light with a higher Vf or a battery with a faster voltage drop which would make your light run only a few minutes in direct drive before going into the regulation. This one would run longer. You may also have something in between.
I'd say that this design, if I understand it correctly, is rather surprising for a light that is supposedly designed for Li-Ion rechargeables.
It is also possible that you abused your batteries. The WF-139 isn't a good charger but since you already have it, you may want to check which version it is.
Here is the post describing how to determine it. The third revision will trickle charge the batteries and can overcharge them if left inside. If you have one of the remaining two, you'd have to search on CPF which one does what. I think the second one doesn't overcharge, I'm not sure about the first one. I don't know if you were systematically overcharging your batteries but if you are sure that they were 4.20V immediately out of the charger, then it seems unlikely to me.
When you have the Quark you should be able to compare runtimes with your batteries and other people results. Note that such runtimes for RCR123s weren't posted yet (I think) and the runtimes in the specification are for CR123s not RCR123s.
You could continue testing your EX10 by measuring both the current and the voltage, checking when it goes into the regulation, etc. but I think that comparing to the Quark should be easier.