Counterpoint: I left a company where I was a Senior Software Engineer and among the most experienced devs of the ~25 they had and joined a company where I was clearly the least experienced dev of the ~10 they had. The CEO of the new company told me that Senior wasn't a realistic title for me in comparison to everyone else and I'd be hired as a Software Engineer—but that I should feel free to use "senior" on my résumé if I thought it'd be helpful.

I thought that was incredibly reasonable. For what it's worth, I do not use "senior" on my résumé and if I'm ever asked why I got downgraded after multiple senior positions I'll happily tell this story.