Well, I'll be the first one to admit that I was naive to expect <5% variance prior to this experience. But I guess you are going to far by framing this as a common wisdom?

In the HN discussion about cockroachdb cloud report 2021 (https://news.ycombinator.com/item?id=25811532), there was only 1 comment thread that talks about "cloud weather".

In https://engineering.mongodb.com/post/reducing-variability-in..., high profile engineers still claimed that it is perfectly fine to use cloud for performance testing, and "EC2 instances are neither good nor bad".

Of course, both the cockroachdb and mongodb cases could be related, as any performance variance at the instance level could be masked when the instances form a cluster, and the workload can be served by any node within the cluster.