A 4% loss is not necessarily a loss. They may have gained $10,000 in income but others gained more. They may have left for a job that paid less because they thought they would be happier. More for one does not mean less for others.
You are assuming a zero sum. If my income increases 10% to $110,000 and yours increases 10% to $55,000, we are both better off although my income increased twice as much as yours. I took nothing away from you and you are better off. However, if others increased more than 10% that may have dropped you out of the middle class.
The median family income in 2021 was $67,463 compared to $58,620 in 2015.
It is not the job of national leadership to maintain everybody's place in the class structure.
If you look at the Treasury Dept/IRS income mobility studies you will see only 42% of those in the bottom income quintile remained there ten years later. Only 69% of those in the top income quintile remained there ten years later.
How are you fixing the "fuck you, I've got mine"? Giving away most of your income?
So, as I stated earlier, the "decline" of the middle class is because more of moving up in income. Of course, that depends on how we measure middle class. If it is the middle three quintiles then the number will always remain the same.