The fun begins when you need to find performance issues in production, where you cannot really use profiler. Then you need to jump into APM tools. Unfortunately it seems there nothing really for that level for free, but take this for example:
https://www.dynatrace.com/blog/code-level-visibility-for-nod...
In my experience, it's very difficult to tie profiling data from generic profilers to specific requests, then to the specific lines-of-code triggering the problems.
This is important because many performance conditions don't reveal themselves all of the time: for example, it's very common that an issue might only be a problem for your largest customers. The context is really important.