I am still trying to wrap my head around lot of these concepts, so happy to be corrected.
One really interesting property of a Parachain I find is the free proof submissions to the relay chain while they are leasing the auctioned slot. The Rollups need to pay gas in Eth per transaction which is more similar in model to what I believe Parathread will look like (i.e. pay per use).
Also, if am not wrong, it should be fairly straightforward to plug in the ETH rollups on top of a Parachain like Moonbeam?