You asked about maintaining wealth and not expanding wealth. Productivity is output per work. If the output per work grows, we need less work to maintain the current output --> workers can chill more. Whether they retire earlier or have a 4-day-week.
Right now that surplus of productivity is just grabbed by the owning class.
once someone pay their fair share of taxes the question is over.
Yeah, right. And if our society wants to take that fair share to expand retirement for everybody, that's cool. And to what a 'fair share' is...that depends. In Germany in the 50ies they basically took 50% of everybodys assets and had an maximum income tax bracket of 95% (which would start at 850k € yearly income today, if they had kept it), literally a max income, if you want. And apparently people thought that to be fair, so there's that.