Well, the ACA stipulates 60/70/80/90% for bronze/silver/gold platinum plans. 90% is pretty high but I'm sure there are "some pre-ACA plans" that pay more.

In general, it's preferable for the consumer to "have some skin the game" so that they might negotiate or increase discretion.

The difference between fixed-size copays and 10% of expenses for the top 0.5% of costliest patients is probably a huge number, so the premiums for those patients would logically decrease though their aggregate out-of-pocket expenses would go up. The point is that it will be a future cost for some people who are currently happy about their lowered premiums.

But I actually agree that consumers should have more skin in the game. My issue is that the statement, "My premiums are lowered!" does not imply that, "The ACA saved me money!" It's more complex than that, and it's plausible that many of the people with lowered premiums are getting a worse deal here.