Do you have an estimate of how much time (Man hours) is devoted to these
tasks you describe?
We have a development LPAR that we use for that purpose.
PTFs are always run for a month in dev, including a full system test,
before they are applied in production.
PTFs are applied monthly in all LPARs during the IPL following the
monthly system backup.
In addition to getting beat up all month by the developers, the full
system test consists of running the previous month's month end process
in dev, and comparing all the reports with production. That's part of
the regular QA schedule.