He never won any really decisive victories or had a long lasting impact. Pyrrhus lost (or won with massive casualties) to Rome, Carthage, Sparta, Argos, and Macedonia. Why was he considered second to Alexander by Hannibal if this was the case?
https://www.reddit.com/r/AskHistorians/comments/97itlo/why_is_pyrrhus_of_epirus_considered_a_great/
You may be interested in this very similar question from a year ago. While it doesn't necessarily directly answer the question, there are a few comments you may find interesting, as they include a few quotes from the Roman sources on Pyrrhus's legacy. The comments by u/cefalopodul and u/the_dinks specifically.
It looks like you're probably familiar with the quotes though. This question seems to get asked a lot without more in depth answers.