This entire post reads like "you probably don't actually have big data".
What do these blockchains do that have to keep data around forever, with high throughput, and need to expose it quickly do? Are you saying they should delete parts of data in the chain?
Seriously, I've spent my career working on big data systems, and while the answer is sometimes "yes you need to delete your data", I don't think that's going to always work.
And what about these blockchains? The full history of Bitcoin blockchain is less than 500gb, so for any analysis just getting a machine with a terabyte of RAM is both simpler and cheaper (once you include dev+ops time) than doing any horizontal scaling across multiple machines with "Big Data" approaches.
"You probably don't actually have big data" is a very valid point, not that many organizations do - most businesses haven't generated enough actionable data in their lifetime to need more than a single beefy machine without ever deleting data.
Bitcoin is notoriously slow. I don't think it's a good example of a high-throughput system. There are chains out there with 100x the number of transactions per second than that of Bitcoin. https://realtps.net/
What do these blockchains do that have to keep data around forever, with high throughput, and need to expose it quickly do? Are you saying they should delete parts of data in the chain?
Seriously, I've spent my career working on big data systems, and while the answer is sometimes "yes you need to delete your data", I don't think that's going to always work.