rough proportion to what they pay in. The more you make and pay in, the more you get out in benefits. We have a cap, so someone making $1m pays the exact same amount into the system as someone making $165k (or whatever the current limit is), but they both get the exact same benefit too because the contributions and benefits max out at the cap. Now the contribution vs. benefits structure is progressive (as an example, a high earner might pay in 5x as much as a low earner, but only get a benefit that is 3.5x that of the low earner), but it's still directionally aligned... the more you pay in, the more you get out in benefits. Everyone is theoretically paying into the system to fund their OWN retirement benefit.

If you remove the cap, all of the sudden rich people will be paying huge amounts into social security, but (presumably) only getting a modest social security benefit (same benefit that they currently get). So in that scenario the rich are not just paying for their own retirement benefit, they're also paying for a bunch of other people's retirement. Hence the "retirement welfare" description.