On the more pessimistic end, AI will replace us and we'll be sent to the coal mines.
On the possibly most optimistic end, living standards are a composite of many things rooted in reality, so I'd say the actual cap is about doubling of life quality, which is not nothing, but not unprecendented if we look at the past century and a half.
There is no long-term time scale in which humans running things do not obliterate each other or end up sitting on a planet filled with trash.
Either we figure out how to colonize other planets or we hand over the reigns to something that can plan long term and not be irrational.
Maybe if we figure out immortality it might work, but with the short life span of a human there is no way to not be short-sited or eventually end up with the wrong person in charge the button.
Honestly, I feel like with the recent progress of AI, it's a realistic scenario to assume it will replace mpst knowledge workers in the next 5 to 10 years, probably won't replace researchers and other elite intellectuals, and won't even make a dent in the world of physical labor.
In that world, I see AI as harmful, but the people in charge won't, as they are directly benefiting from it.
We live in number-go-up capitalism. A good analog is the housing situation. The ever increasing price of real estate means that the total amount of wealth goes up, so it's seen as a beneficial process by the elites. The rest however will find that they need to dedicate a larger proportion of their income towards getting a roof over their heads, and think this process is bad.
Nowadays, the possibility building a life that would've been considered middle class half a century ago from scratch is available to like 10% of workers, working mainly intellectual jobs.
AI in the future will reduce the proportion of these people by taking away their high paying jobs.