Contributors might be disincentivized to use the Assisted-by tag for the reasons you mentioned, but at the end of the day, commit provenance is still an honor system. We can't force people to be honest, but we can encourage it by requesting they tag appropriately.

It would be dishonest to take credit for work that is not my own, so I just don't. If an automated tool (e.g., a linter) or a person contribute to a commit in a significant way, I credit them. I've never used the Assisted-by tag because it's relatively new and its scope is unclear, but I provide appropriate context in commit messages to make clear what the extent of the contribution was.