Having run a medium size Spark cluster, I'm not sure I agree.

If you have 80-100% utilization for a month, perhaps, but the beauty of Snowflake is that you can spin up a 3XL warehouse for a few MINUTES to get answers fast, and then shut it down again and don't pay anything.

Saying "you could run it on self-managed Spark/Oracle/Hive/SQLite" is approximately the same argument as saying "I can run a web server cheaper myself than paying Amazon for an EC2 instance" -- there are cases where that is true, but there are many, many, cases where the "on demand capacity" is the bigger benefit.