I want to address this issue pointwise, hence prepare yourself for long valley.
Tsunade never had Danzo under her check, Danzo actually killed the frog who was supposed to transmit the message to Naruto. Tsunade never tried to control Danzo, so this point is invalid.
About the first statement it looks like a childish argument to me. Second one I already proved it wrong, we can't simply deny the fact that Danzo safely killed that frog and caused delay in letting Naruto know about status of Konoha, under her nose. So, I don't see any surveillance here.
Danzo wasn't Hiruzen's blunder. Hiruzen can do at least better than many other people who fought against Pain. I agree Tsunade did an excellent work, but that wasn't enough.
She failed, I am not talking about Tsunade being bad or good hokage, as it is matter of opinion at the end of the day, but we can't deny the 'fact' that she failed to protect Konoha when it was in trouble despite the fact that she was 'one of the three legendary sannins'.