Gini coefficient may be the most commonly used statistic but it is not sensitive to current conditions in the US (https://www.investopedia.com/news/measuring-inequality-forge...). The palma ratio does indeed show increasing inequality since the 90s (https://ourworldindata.org/grapher/palma-ratio-s90s40-ratio?...). Also wealth inequality is another place to be looking, especially if you're familiar with Piketty's body of work which points at it specifically (https://www.visualcapitalist.com/wealth-distribution-in-amer...).

You know what they say about lies and statistics.