Kelly is an awful candidate who lost by over 10 in 2020 under the backdrop of the Democratic Presidential Primary, and lost by 10 again this year under the backdrop of abortion. Maybe the main problem is that he’s just a horrific candidate.
I would advise against people extrapolating too much from this result for this reason.
If this was an isolated incident, I'd probably agree with you, but it just isn't. Republicans have consistently underperformed in general elections after 2020. This is part of a systemic issue with the GOP.