While I agree that 1-5 amazing, there were a few standalone seasons that were also very good. I think it's season 11 where they are trying to stop Gods sister, and that was a banger. A redeemed Metatron trying to convince Chuck not to give up on humanity is peak Supernatural.

Of course, then they completely ruin that excellence with the plot twist involving God in the last season.

I think the show had two perfect series finales, S5 and S11. The actual finale got ruined by COVID, so I'd cut them some slack if the rest of the season wasn't terrible.