Launchd process behavior
Something definitely doesn't sound right with what you're describing. Most descriptions of Launchd describe it is mostly doing nothing as described in this article titled: What Is launchd, and Why Is It Running on My Mac?:


  It’s very rare for launchd to take up many system resources, and when
  it does happen, rebooting your Mac is usually enough to fix it.
  Occasionally a buggy program trying to launch faulty daemons can cause
  launchd to use up a bunch of CPU. If you’ve installed something
  recently, try removing that and seeing if it helps.


You can check on what it's doing with this command:

$ launchctl list | head
PID Status  Label
-   0   com.apple.SafariHistoryServiceAgent
-   0   com.shazam.mac.ShazamHelper
-   0   com.macpaw.CleanMyMac4.HealthMonitor
36706   0   keybase.updater
702 0   com.apple.Finder
1256    0   com.apple.SafeEjectGPUAgent
64713   0   com.apple.quicklook
-   0   com.apple.parentalcontrols.check
-   0   com.apple.PackageKit.InstallStatus


From the sound of it with the logs being written to it sounds like Launchd is logging debug level on either one or more processes on your system. You can read more about changing the log level here:


How do I activate launchd logging on OS X?



There's also this aSE Q&amp;A titled: New stats file created every 20 seconds in /var/log/com.apple.launchd.peruser.94? which doesn't have an answer but does describe and show another issue related to Launchd where it is excessively logging files.