It's not the intrinsics. It's the whole list of special one-off factors at play. By the way, Greece started privatization in the 90's, not in 2015.
When there's no external assistance and the government pays loans out of its budget, it means it's not paying something else internally, usually some business it owes money to. If you feel that that is a non-factor in economic destruction and therefore tax receipts, then sure, have your own numbers.
The question is how the country would fare if the debt wasn't there, but the rest of the economy was functioning properly.
As a disclosure, I am Greek and have intimate knowledge of facts of the ground. If we can't agree the past six months are not "normal" there's very little to talk about.