Greece Austerity
1) Austerity was demanded by all of Greece's creditors. In fact several countries were far more keen on punishing Greece than Germany.
Poorer than Greece: the EU countries that reject a new Athens bailout
theguardian.com/world/2015/jul/09/poorer-than-greece-the-eu-countries-that-reject-a-new-athens-bailout
2) You (and many Greeks) seem to have a very strange understanding on how negotiations between two countries work. Tsipras promised that he would end austerity and Euro would keep the Euro if the Greeks voted No in the referendum. All European politicians stated this was not an option. Greece could either accept austerity or leave the Euro. Tsipras was simply dishonest about how the situation looked like. He told the Greeks that they could have their cake and eat it. No country was willing to make any concessions to Greece, and if they had held a referendum in any European country, probably a majority would have voted to kick Greece out of the Euro.
Of course, Tsipras could have drawn the conclusion that having failed to get any concessions, in order to respect the referendum, he'd have to lead Greece out of the Eurozone. However since polls indicated that the Greeks also wanted to keep the Euro (which in return just shows you how bizarre that whole referendum was) he decided to agree to the demands. That was his decision, no one else.
Greece lost 30 % of its GDP with not real prospect for recovery ever because the Euro is not a currency*,
The Greek economy was artificially bloated by reckless public spending and other measures, it is now closer to what it actually produces. It will take Greece many years until it recovers to the standards it held pre 2009, but this time, it will be honesty earned. And as a bonus, it looks like they have learned how to properly fight tax evasion and organize a proper bureaucracy. I just pity the young Greeks who have to pay the price of their parents excesses.
A fellow Greek student of mine told me an interesting story about his small home town. A few years ago, he passed the very difficult test to get a job in the Greek bureaucracy. Yet there are currently no positions open. The one spot he could have applied for is held by a middle aged man who got his job two decades ago because he was friend with the local mayor. The position requires a university education, yet the man hasn't even finished high school. According to proposals by the Troika, such obviously unqualified civil servants should be fired, but consecutive governments have refused to do so. My fellow student decided to leave the country eventually because he has given up hope that anything will change.