If your potential write amplification for a single operation is anywhere remotely near a factor of 1 million, you have a serious problem and need to completely change your approach to the problem, and use different data structures and algorithms.

Hardware hasn't gotten that much faster really. PCIe flash cards started to get used over a decade ago -- yes, modern storage is better than those were, but not by a huge multiple. And meanwhile max CPU frequencies today aren't much higher at all. What we have instead is more cores. And a lot more RAM per box. Faster networking, sure. But none of this lets you get away with massive write amplification from choosing an overly-naive algorithm.

And iops aside, even just the storage capacity from full inbox materialization (along with necessary indexing overhead) will bankrupt you, especially on that blazing fast storage you keep talking about. Keep in mind everything needs to be replicated to multiple regions / data centers for DR/HA, as well as keeping the data closer to users to lower the latency.

I'm not making "assumptions" that I need to "refresh". I've literally spent the majority of my career working on this stuff at extreme scale, both in 2010 and today, and all times in between.