Comparing Osimhen so far this season with Haaland's last four seasons (so including stats from the weaker German league as well as his stats so far in England), per 90 and without penalties.
Osimhen - 1.03 goals, 0.71 xG
Haaland 19/20 - 1.10 goals, 0.74 xG
Haaland 20/21 - 0.93 goals, 0.76 xG
Haaland 21/22 - 0.75 goals, 0.62 xG
Haaland 22/23 - 1.06 goals, 0.72 xG
So he's effectively having a Haaland-level goalscoring season. And while his previous two seasons weren't as good, they still stack up just fine compared to some other top strikers we might have an interest in.
Osimhen 20/21 - 0.57 goals, 0.61 xG
Osimhen 21/22 - 0.64 goals, 0.48 xG
Kane 19/20 - 0.56 goals, 0.38 xG
Kane 20/21 - 0.55 goals, 0.49 xG
Kane 21/22 - 0.36 goals, 0.43 xG
Kane 22/23 - 0.63 goals, 0.45 xG
Obviously Kane was performing in a tougher league across those seasons, but then he was also a lot further along in his development at 26-29 years old than Osimhen at 21-23.
And because people sometimes make the "Lukaku tore up Serie A as well" argument as a diss, a comparison of the two to highlight the difference.
Osimhen 20/21 - 0.57 goals, 0.61 xG
Osimhen 21/22 - 0.64 goals, 0.48 xG
Osimhen 22/23 - 1.03 goals, 0.71 xG
Lukaku 17/18 - 0.50 goals, 0.39
Lukaku 18/19 - 0.51 goals, 0.44
Lukaku 19/20 - 0.51 goals, 0.43
Lukaku 20/21 - 0.56 goals, 0.57
So whether for United or Inter, peak Lukaku's best season wasn't as good as the worst of Osimhen's three at Napoli thus far, let alone his best in which he is scoring at quite literally twice the rate.
In this case I don't think the numbers lie, this guy is a straightforward elite striker.