What decline? He had two career years then seemed to level off between 115-125 wRC+ or so. I think you can expect a year or two to be up or down from there, but he's been pretty consistent. That's like saying Mookie Betts declined after his age 25 season in 2018 because he had a 10.2 fWAR and went back down to 5.8 fWAR.