Putting aside for a moment that 30% of nothing is nothing, where are you even getting this idea that someone got a 30% tax reduction?

Look at the plot you shared "Personal Taxes: Federal Income Taxes by Quintiles of Income Before Taxes: Third 20 Percent (41st to 60th Percentile)"

2015: 1854

2016: 1954 (+100)

2017: 2170 (+216)

2018: 2676 (+506)

2019: 2519 (-157)

What about these numbers makes you think that the third quintile on average got a 30% tax cut?