I don't think the show has fallen off per say but I can see certain things already going into motion. Stella keeps falling for the "wrong guy", wouldn't shock me if her and Columbo hook up.
Columbo is the obvious antagonist of the show now so a lot of the season will be wrapped up into his story line. They also said currently the show is in '64, Malcolm was killed in 65 so it will be interesting if they sped it up and kill him off in the season finale.
My biggest gripe with the show is every season, damn near every episode its always centered around bumby going on suicide missions to make Harlem his. Like him stealing money that was supposed to go towards helping the city rebuild to pay off his drug debt was cringeworthy.