I think the issue is focusing on super as begin the ONLY way to save for retirement.
The cost of the tax forgone on super is large. There is a cost with lower services / infrastructure spending or higher taxes.
By your argument once someone's super balance can pay them the equivalent of the aged pension for say 25 years then the system has done it's job?? Is it efficient to provide 20% of those contributing to super over 50% of the tax benefits?
You can save for retirement either in or out of super. If you aren't employing any gearing through investment loans, margin loans and geared property investment, you'd be better off for retirement savings purposes putting the money into super and having earnings taxed less.
I understand the cost of the tax foregone on the super is large, but the savings in future pension expenditure will also be large.
I don't know what the 'equivalent of the aged pension for 25 years' stuff is all about - the aged pension is not a comfortable retirement where one can enjoy themselves and help family with things like private tuition fees, or doting on grandchildren at Christmas. If that's all you want out of a self-funded pension that's fine, but I don't personally want to be eating sausages and mash and watching the 6 o'clock news for entertainment every night between leaving the workforce and dying. Money to live, not exist, would be nice.
As far as over 50% of the benefit going to 20% of the people? I don't think much about the tax system is fair at all - I think the rich already pay far too much to support the poor thanks to excessive middle class welfare that has done nothing but keep us one of the most expensive places in the world to live. I'm not that disappointed that the wealthy are getting a bigger percentage advantage, because it would still seem to me that these people pay more in taxes than a dozen people at the opposite end of the spectrum. What they earn is irrelevant, it's what they pay in taxes as a dollar amount that shouldn't be ignored.