While it's true that Rails is sinking under the weight of its own cleverness, and is clearly the old hotness, this has nothing to do with Ruby the language.
Rails' problems are its own, and Ruby's limitations and problem domain are well known.
This is a terrible blog post by someone without much perspective. I award it no stars.
The author of the post at no point blames Ruby for Rails' failings... But also I'd contest your argument that they're unrelated. Ruby is what enables the too-clever metaprog that make Rails stack traces so opaque. Also Rails has almost certainly been the single largest drive of Ruby's growth and popularity - observe the significant overlap of core contributors to both projects.
Rails' problems are its own, and Ruby's limitations and problem domain are well known.
This is a terrible blog post by someone without much perspective. I award it no stars.