This is hack-level misuse of this statistic, comparing a career counting stat total with the "awful" assessment in a single season. That would be like saying a player with 100 career RBI is elite because 100 RBI is a lot for one season. On top of that, even a cursory glance at his numbers would show you that a whopping -1.67 of that -2.11 came in 2016 alone, and that every other season he's been within -0.5 to +0.5. This is just a comically bad take and/or fabricated narrative; it's like how you'd expect cable political news to use data.
Also, suggesting that we should be concerned about playoff performance because of leverage index is, at best, a complete misunderstanding of leverage index.
And it's not a great statistic, anyway. It's really a different expression of WPA, which is useful in a descriptive way that same way RBI or runs scored is -- meaning it can be a really compelling part of say, and MVP conversation, but an incredibly bad number to use to make any sort of projection or assessment of talent.
The reason this stat is rarely talked about is because it's been shown to have practically no predictive value, meaning it would be a bad idea to make decisions based on it, or similarly, to be "worried about him in the playoffs."