Dell Inspiron 5759 had AMD graphics card problem

I have a Dell Inspiron 5759 laptop which includes, as standard, an AMD Radeon M335 graphics card. Out of the box I immediately noted that Dell’s own Support Assist program, which runs various tests, was testing the integral Intel 520 graphics not the AMD card It appeared that the AMD card wasn’t doing anything. I raised this with Dell Support who tried using Unigine Heaven to test the graphics. It was found that you get slightly better results on the Unigine test, if you disable the AMD card in Device Manager, and only use the Intel Graphics.

This puzzled Dell Support and over the following weeks they spent more than 8 hours (really!) changing drivers, looking at switchable graphics, and numerous other things, but still the graphics card tests run better with the AMD card disabled. Eventually Dell referred to the issue to a higher level of support and the answer came back: the AMD card is working fine. When I asked how that could be, if the tests give better results when the AMD card is disabled, they say the card only works in cases of high graphics demand. But what are the Unigine and other tests for, if not to create high demand? They didn’t answer that, or specify what test or application would work better with the AMD card enabled. They refused to progress the matter further.

Is Dell’s response credible? The laptop works OK in everyday use, but I have a couple of months of warranty left and I’m not sure whether, or how, to progress the matter further.