Kevin in Season 5 didn't really get worse to me
I hear people complain about Kevin getting worse in Season 5, but he doesn't really change much.
Mission Ed-Possible: Kevin did laugh at Double D, but so did the other kids, and Kevin had a right to be mad at Double D stealing his bike.
Every Which Way but Ed: This was a flashback episode.
Boom Boom out Goes the Ed: Kevin was bossed around by Rolf for the entirety, so he didn't have much opportunity to be an asshole.
Cleanliness is Next to Edness: Absent.
Out with the Old, in with the Ed: Kevin was being a dick alongside the other kids, so he didn't stand out.
I am Curious Ed: Kevin was harmless here.
No Speak Da Ed: Again, Kevin was harmless here.
Cool Hand Ed: This episode was primarily focused on the Eds, Jonny, and Plank.
Too Smart for his Own Ed: Kevin wasn't really much of a jerk in this episode outside of him treating Double D like an idiot, but the other kids are guilty of that as well.
Who’s Minding the Ed: Kevin didn't do anything to warrant Ed and Eddy messing with him.
Pick an Ed: Kevin was nice to Eddy disguised as Carl.
This won’t Hurt an Ed: It was nice to see Kevin get tortured by Ed and Eddy since Kevin blackmailed Eddy for no reason in "Your Ed Here".
Truth or Ed: Kevin and the kids had lies written about them, so they're justified in their anger.
Tinker Ed: Kevin had every right to be pissed off by Jimmy and Sarah since he was trying to study.
The Good, the Bad, and the Ed: Kevin was in the background alongside Nazz and Sarah.
Tight End Ed: Kevin had a team filled with people who weren't cut out for football, so his anger was justified.
Tween a Rock and an Ed Place: Kevin did nothing this episode.
All Eds are Off: Kevin took part in the bet and lost. He didn't really act like a dick here.
Smile for the Ed: DEFINITELY an asshole here!
Run Ed Run: Absent.
A Town Called Ed: Kevin was pretty smug in this episode, but it's in-character for him to not invite the Eds to his house and make fun of them at the end.
A Fistful of Ed: Kevin did nothing assholish at all.
If he really did become more of a jerk, he'd be acting like how he did in "Smile for the Ed" for the entirety of the season.