I think the difference here is in the use case, and I think it boils down to "ETL" vs. "ELT". If you do ETL, and your analyst team runs a few ad-hoc queries, then the pay-per-query approach makes a lot of sense. It would agree that it's "ultra-efficient".
If you do "ELT", where you ingest fairly raw data on a continuous basis, and then run complex transformations within your data warehouse, then the "buy a cluster" pricing will win. The data loads (we've seen load frequency up to every 2 minutes) require resources, and then so do the transformations.
===================
side note:
When it comes to utilization, I always have to think of this great research paper by Andrew Odlyzko:
http://www.dtc.umn.edu/~odlyzko/doc/network.utilization.pdf
"Data networks are lightly utilized, and will stay that way"
===============================
Agreed that most warehouses sit at 30% utilization. The customers we work with have more utilization than 30% though. That's because they're continuously ingesting data, transforming it within Redshift, and then lots of ad-hoc queries by analyst teams and data services that feed other applications. If you have a business that runs on a two or more continents, then you don't even have downtime during US nighttime, as Europe, Asia, etc. are running. And so in those cases, we've seen that customers don't want any surprises and would rather pay for the cluster. Predictability becomes more important than paying the lowest amount possible per query.
---------
I'm a co-founder at https://www.intermix.io - we provide monitoring for data infrastructure