I dont think American tennis is in the depth of despair, I dont think you can rule out Coco and Amanda just yet as GS champs in this era, I am with the consensus that Gauff is over-hyped but both her and Amanda are still young and have loads of time to improve. I think in about 18 months we will have a better idea of where they are both heading. There is also the possibilty of Kenin returning to her 2020 form (unlikely at this point though)
That said, I agree with the broader view that American tennis is not like it once was (Davenport, Williams etc), it does make you wonder where all this USTA money is going? Two promising players and only two slam champs in the past five years (both of whom have not lived up to expectation) is not a great look for an organisation with money to burn for the development and growth of American players. In contrast you have these Europeans who dont have the luxury of coming from countries with big tennis federations (where its more grass roots) achieving great things.