I think the presumption that's differing here is query workload.
An OLAP database is, in the default case, an always-online instance or cluster, costing fixed monthly OpEx.
Whereas, if your goal in having that database is to do one query once a month based on a huge amount of data, then it will certainly be cheaper to have an analytical pipeline that is "offline" except when that query is running, with only the OLTP stage (something ingesting into S3; maybe even customers writing directly to your S3 bucket at their own Requester-Pays expense) online.
An OLAP database is, in the default case, an always-online instance or cluster, costing fixed monthly OpEx.
Whereas, if your goal in having that database is to do one query once a month based on a huge amount of data, then it will certainly be cheaper to have an analytical pipeline that is "offline" except when that query is running, with only the OLTP stage (something ingesting into S3; maybe even customers writing directly to your S3 bucket at their own Requester-Pays expense) online.