Yes, but PaaS is more about putting an entire application framework into the third party system than it is about putting individual functions.
If you change something you still have to upload the entire application rather than a tiny element and breaking changes are more likely.
Serverless is more about coding for each individual event you want to respond to than it is about the servers.
And with PaaS you still have to think about provisioning and still have to think about uptime and still have to think about a bunch of stuff that you just don’t with serverless.
Quick example: a friend built a mobile game with a heroku backend built with rails. They launched, and found that the application had provisioned about 10 times the number of servers they were expecting. They found a bug and re-deployed of course, but still had scaling issues.
Serverless avoids that issue. You’d find that one or two of your functions might be taking longer than expected, but not the whole application.