Austerity is not the same as entitlement reform. Austerity is targeting a surplus regardless of the costs, which in this case tanked GDP faster than they could pay off debt, meaning the dept to GDP ratio got much
worse.
Entitlement reform is an entirely separate thing.
And given that Syriza has, in fact, slashed pensions and raised the retirement age, they are clearly willing to do that. Since they are a new party dedicated to breaking with the past governance, they are also willing to embrace change. And since they won the election, this means the population gave them a mandate to do exactly that.
The old party, which was responsible for many of the entitlements in the first place, sure as heck wasn't willing to change Greece. Complaining about the new party seems strangely misplaced.