From what I've seen, at many Phoronix benchmarks there are big differences between the results of the various benchmarks. IMHO either there are not enough "benchmark runs" to get accurate results or he uses the average between the "benchmark runs".
There are dozens process running or sleeping in the background especially when running a "Default Desktop". How do you know that something else didn't decide to run or to sleep when benchmark was running.
But it is hard to tell without some profiling/perfomance information which would make the benchmarks actually helpful to developers or to distro maintainers.
As said above and it was done on a laptop mobile GPU, Ideally it would be better on a high and low end PC.
Remember hardware is not free and high end hardware costs a lot.