The lounges are not crowded with Platinum and Centurious cardholders, they are crowded with their entourages. Get rid of the entourages and you'll have plenty of space in virtually every lounge aside from peak periods where the lounge may fill, but not overflow. I've written more than once that the easy cure for overcrowding is
1. primary cardholder only plus 1 guest during most time periods
2. no families/children - 1 guest means one spouse or one child over 16 but not everyone together
3. no guests when the lounge is above 80% capacity
4. no corporate paid cards, ie tech bros with cards issued by their employer - personal Platinum or small business cards issued under the business owner's name only
5. no secondary card accounts - lounge access is only included with full retail payment of the $695 annual fee, discounted secondary cards should not include lounge access

Amex will never cut back on the number of cardholders just to prevent lounge overcrowding, that would be a crazy decision as lounge access is just one small feature of the entire cardholder book of amenities.