This is a weird response to a weird article. The original article doesn't define its terms and, as Robby points out, that makes it hard to critique. If a language is only "serious" if it can scale infinitely for all use cases then sure Ruby isn't serious - most languages aren't.
That said - this response and the critique seem to basically agree. The critique can be summed up as "Ruby doesn't work forever" (and so it should never be used) and this is saying "Ruby doesn't work forever" (which is fine). I could almost understand this post as saying: 'Ruby isn't serious and that's not a problem for anyone who uses it.'
I will say that I found it funny that the original article attacked Ruby for being all the way down at "18th place" (This is inaccurate - it's 14th in 2024) on the SO dev survey - while talking up Scala which is 9 places further down on the survey[1].
[1] https://survey.stackoverflow.co/2024/technology#most-popular...