While much less common than 10 or 15 (err… even 20) years ago, you still sometimes hear MySQL being called a “toy” database. The good news is, when somebody says that, they’re admitting ignorance and you can help educate them!
Recently, a fellow IBMer submitted a pull request (and bug) to start having MySQL support on Z Series (s390x).
Generally speaking, when there’s effort being spent on getting something to run on Z, it is in no way considered a toy by those who’ll end up using it.