Just because there are ways of dealing with something, it doesn't mean there's an imbalance. it its *more difficult* on average to counter a BLU than it is to counter most other jobs. It doesn't mean you CAN'T counter it, but it requires more skill and effort on the non BLU's part. That's when you can identify an imbalance. Something doesn't have to be unbeatable to be imbalanced. It's not a crippling, staggering imbalance, but it's enough of a problem to notice.
You just contradicted yourself... The fact that BLU is not unbeatable means that it is not overpowered and therefore there IS a balance to it. If you haven't found the way to create that balance yourself, then it's obvious your problem is your lack of forethought to a typical strategy that a BLU would follow.

I challenge ANY BLU to take me on, I will prove that you are likely weak. I know that I may not win every challenge. If I did, a bunch of people would say there is an "imbalance that exploits BLU's weak points." And that would be called a contradiction.

I challenge every and all people to explain their point or prove to me that there is a problem with the way things are. But don't get disappointed when I KICK YOUR ASS.