Agreed this looks like it should be made default behavior. This has affected many people I work with, and even with searching, this ticket never came up. I only found out about it by making a ticket myself. This issue looks like it has generated at least 3 tickets in this bug tracker, and the agent is raising memory errors during normal usage, which still smells like a bug to me.

I ran gpgconf --kill gpg-agent and then the suggested command for i in {1..10}; do gpg -v --no-tty --verbose -o - encrypted.gpg 2>mylog.$i > /dev/null & done. (I was already running with --verbose, does -v add something else?)

I made a large file for testing, but it doesn't matter. There's an arbitrary parallel limit where gpg will crash.