I think it is fair to say from your assessment that you don't watch much football besides the Colts. Kelly admittedly wasn't at his best the past 2 seasons, but he was far from the worst C in the league. I know PFF can be taken with a pinch of salt, but his overall grades were:
2022 - 64.3 with 5 sacks and 3 penalties on 1092 snaps (136.5)
2021 - 56.9 with 3 sacks and 6 penalties 907 snaps (100.8)
2020 - 69.0 with 2 sacks and 1 penalty on 1007 snaps (335.7)
2019 - 73.0 with 1 sack and 6 penalties on 1018 snaps (145.4)
2018 - 74.5 with 1 sack and 4 penalties on 777 snaps (155.4)
2017 - 60.4 with 0 sacks and 0 penalties on 394 snaps (0)
2016 - 72.4 with 0 sacks and 3 penalties on 1018 snaps (339.3)
Overall (177.5)
The figures in brackets are the number of plays per major error (so a sack or penalty)
You can see from their grading, that he has not been to his usual standards the last two years, but this past season was an improvement from the year before. And his past two seasons the number of "mental" mistakes, so the sacks and penalties, have risen quite a bit.
This is a link of the PFF grades of all Centers for the last year. Kelly is ranked 16th.
https://seahawkswire.usatoday.com/ga...-rankings-pff/