I don't use MSE for it's detection rate, I use it because I know it's not going to break anything or have compatibility problems.
It's also not the only one which had a low detection rate at some point in the testing. You could argue that in July 2014 several A/V's had rather poor detection rates and in fact throughout the testing the detection rates varied quite a lot with their random samples. If anything these results show just how varied detection rates can be regardless of A/V vendor and that A/V's in general shouldn't be relied upon for protection.