Yes, but often only for major bugs that are deemed worthy of developer's attention. In practice it's not always so great. Read systemd's bug tracker, not all user-reported bugs get fixed to those users satisfaction, neither by redhat nor by systemd. Systemd is too big and developers refuse to accomodate everybody.

Shell scripts are tunable to the specific system. If a rare bug is in a shell script, I can usually find and fix it, unless the script is insane, in which case I can write a sane one.

If a bug is in systemd, I can't easily fix it myself. I now have to fight upstream to recognize my issue and fix it for me. I don't have a good experience with this. Nowadays I'd rather write a small script to work around that bug if possible. Much faster and much more effective.