The highest marginal tax rate (the report you provided) has nothing to do with how progressive or not progressive a tax system is. You can have a high marginal rate and not be progressive, or a low marginal rate and be highly progressive, or any combination of the two.
A salary for an individual is not the same as the salary for an income group who always has different members. Here’s a quick back-of-the-napkin example of a company:
2000: A company has 20 employees each making $50,000 a year.
2001: The company gives everyone a $10,000 raise, then hires 5 more people at $50,000 a year.
2002: The company gives everyone a $10,000 raise, then hires 5 more people at $50,000 a year.
2003: The company gives everyone a $10,000 raise, then hires 6 more people at $50,000 a year.
2004: The company gives everyone a $10,000 raise, then hires 8 more people at $50,000 a year.
2005: The company gives everyone a $10,000 raise, then hires 10 more people at $50,000 a year.
In 2000, the bottom 20% of employees are making $50,000 a year. And at the end of 2005, the bottom 20% of employees are still making $50,000 per year.
So would you say that the company is not paying the employees more? Of course not! Every employee gets a $10,000 raise every year. The people making $50,000 a year are now making double that. And no one’s wages have stagnated, even though the top 20% have been making the same salary for five years.
That’s…not how math works. You can’t calculate the percentage of their own income unless you know their income and how much was collected in taxes.