The number of good, distinct papers someone produces does correlate pretty strongly with their expertise or (a better goal, I think) with the impact a researcher has on their field and on the world. But many of the greatest advances have been made by researchers who are only known for a few very important publications — sometimes only one.
Any idiot can crank out dozens or hundreds of worthless or redundant papers and get them published somewhere, and can even collect a large number of citations, many from friends and co-conspirators. So you can’t just look at the paper count or even the citation count and treat that as a reliable indicator of quality and impact.
See also this interesting paper with criticism of the current misuse of citation analysis: How scientometry is killing science, https://www.geosociety.org/gsatoday/archive/24/12/pdf/i1052-5173-24-12-44.pdf