EPTI think that most players cannot actually rate the balance from their results because they cannot compare their skill to that of their opponents in most cases.
If all players' skill was rated in a rating between 0 to 100, their results should be explainable by comparing their skill and the matchup balance to their opponent's skill. The other way round, this means that players cannot rate the balance of a matchup when they don't know their or their opponents skill levels.
If a Zerg player wins 50% of his games against Skill-80-Terrans, does that mean that he is equally skilled? Not if the balance is unknown. Maybe he is way more or way less skilled but the matchup is not balanced.
Thus, you have to know a player's skill to get information about the balance by looking at his matches. Most players who flame and whine about balance can't know their or their opponents' skill, for example some Zerg might have been massively overrated and now think their race was broken because they loose against players they had a chance against before the patch.
The only players we can rate more or less accurately are top players. The beta might not be old yet but there already are players of each race who have exeptional results such as Lucifron, Dimaga, DeMuslim and several others. Those are the only players who's skill can be quantified as they must be more or less close to 100 (maybe not of what is possible overall but what is reached yet). So if you check their results, you can draw an approximate picture of balance.
Sure, this method can't always work and won't work for balance amongst all skill levels. If there, for example, is something you have to do in order to maintain a chance of winning in a specific matchup that just requires a certain base skill but does not really bother professional players, a matchup can be balanced for top players but not for the majority of the community.
(Let's say players have to stack Mutas to win against Terrans, very good players won't have a problem with that, a little worse players might be struggling with their multitasking and have a disadvantage over Terran, bad players won't be able to do it at all, but on their skill level it possibly won't be so important anyways :D).
All in all, I just think that there is way too much whining going on from players who don't even try to be objective about their games. They don't see "oh wow I got supply blocked right before the push so I lost", they just see "I lost again against this stupid race!" and complain about it in all forums they know.
