Could possibly be linked to where you stood, I have not heard this years so cannot comment to much. But what I do know is sound (especially outdoors) can vary massively depending on where you are stood. It is almost impossible to get perfectly balanced sound across the whole area, especially with the large line array / floor standing bass cab setup they are using. This is also usually very noticeable at festivals. They do usually give a good level of balance and pressure to most of the crowd though from what I know.
Bass is always notoriously bad at throwing out to the back of large crowds too, a large part being that the crowd physically absorb the soundwaves, so one method to counteract this, is using more powerful bass cabs, this does lead to the bass appearing to overpower the rest of the audio near the front though, plus, being so far forward you are not usually in the direct path of where the majority of the audio is getting sent out from hanging line array speakers which carry the mid and treble parts of the audio, making the issue worse to your ears. It is not always possible though, to be stood in some of the better positions to get the most out of the audio setup. In the general area of the control booth is usually a good shout though, especially if that is where the audio is being mixed from. As that means that whole area 'should' be flooded in pretty decent sound.