Can a 30+ HR season be bad? At first I thought that no, a 30 HR can't be bad. And then I took one look at Rougned Odor's 2017 season.
Rougned Odor was in his 4th year with the Rangrs in 2017. He was a good prospect back in 2014, and in 2016 he had showed why. In 2016, Odor slashed .271/.296/.502 with 33 HR. He had never drawn a big amount of walks, but in 2016, he only had a 3.0% walk rate. He was never a good fielder, always being below average. He was coming off of two productive seasons at the plate in 2017, so the expectation was that he would keep climbing. He did not.
In 2017, Odor slashed .204/.252/.397 with 30 HR. That gave him a wRC+ of 56. He was 44% below average! Below is a picture of every 30 HR season ever by wRC+:
Can you see the top that is near 50 wCR+? That's Rougned Odor's 2017 season. He was just bad a hitting, he was methodically horrible. Well, at least his defense made up for it. Right? Wrong. He was still below average in defense as well.
In short, Rougned Odor's 2017 season was horrible, even though he hit 30 HR.