Kimbrel's "problem" this year is that his BB/9 has spiked to 4.2, while is was 2.0 and 2.7 in prior years. He's actually striking guys out at a higher rate and giving up hits at a lower rate this year, so he is still plenty dominant.
I don't think 60 IP from any closer is worth what the elite ones make, but Kimbrel's contract is pretty far down the list of problems for this organization.