OK, they said actually said the phrase pump the brakes to mean short sharp bursts on the brakes
Ah, OK, I'll have to try using the front more.
I can see there has been some confusion as to the meaning of the term "pumping" here, and it is used for both meanings - (a) Repeatedly pulling on the brake lever to make a spongy disc brake firm up, and (b) On/off action downhill rather than dragging the brake (often used with rim brakes to minimize brake block overheating and brake "fade").
It sounded at first as though you weren't getting any braking power and that (a) was meant, but it now seems more likely that the LBS meant (b) and was not suggesting your disc brakes need to be pumped to actually work.
Anyway, it does sound like you are over-using the back brake if you're getting it to the point it skids, so more use of front brake seems to be in order. To try to determine if the front brake is actually problematic, here's a couple of questions...
* Can you bring the bike to a hard stop using the front brake with only modest pressure on the lever? (Try it at low speed on the flat, not tearing down a hill)
* When you apply the brake, do you feel a slow and even increase in braking power through the range of movement of the lever, or does it feel like there's a "bite" point at which the resistance hardens up.
In my limited experience (having only used hydraulic brakes on one bike, my MTB), hydraulics are better at getting a quick stop (and for stop/go off-road descents), and the cantilever rim brakes on my touring bike are better for finer control of slowing on long paved downhills.