Kimbrel has been overused because Alvarado was hurt and Seranthony is shaky and Soto has never completely established himself as a consistent high-leverage guy (nor Hoffman. Heck, they gave Marte a few shots before he cratered again too).
But it's also the fault of the closer model. Thomson seemed to manage workloads a lot better when the roles were less rigid.
It's also the six-man rotation. Dombrowski did fortify the bullpen at the deadline, and that fortification is Lorenzen. Or Sanchez. And once the playoffs hit, Suarez maybe too. They did not need an extra arm in the pen for the stretch run. They're 17-9 in August!