I can't find a table of conversion rates to compare, but Piroe has a 9.2% conversion rate with the highest in the league having around 14%.
Haaland's conversion rate is 23.3%; Kane is 16.4%.
If you look at team conversion rate, Burnley and Middlesbourough (the highest scorers in the league) have an 11.8% conversion rate. Sheff Utd, who are second, have a 9.1% conversion rate.
I don't think Piroe's conversion rate is that bad; it's not spectacular.
Piroe's xG is 15.2, including 2 penalties, so I'd say he's scoring as many as he should be scoring; He's maybe under-performing a little. He scored 22 goals from an xG of 12.2 last season which is a huge over-performance; perhaps not sustainable.
Bare in mind that he has played 10 games as a winger and #10.
Here's his comparative stats versus other forwards in his league: