alt Hacker NewsCounting words and 们 aren't the same, as they aren't declensions. You add on the syllable rather than actually changing the syllable of the noun itself.
Granted, that's still different from saying that Mandarin doesn't have a concept of plural, but I think the underlying point- no conjugation or declension- is very different from the other languages being discussed.
To be more accurate, 们 isn't a plural marker more because of the fact that it's not productive[1], rather than the fact that Chinese doesn't have declension. If 们 were able to be suffixed to any noun to make it plural, then you could consider it to be a plural marker, even though the noun isn't technically declined. That's not the case anyway though, since 们 can only be used with a closed set of pronouns or in a limited way to refer to groups represented by the noun its attached to (in this sense it's more of a metonymic[2] marker rather than a plural marker). For example, 白宮们 can be used to translate "the White House" when it refers to the President and his administration, and cannot be used to mean "white houses".
[1] https://en.wikipedia.org/wiki/Productivity_(linguistics) [2] https://en.wikipedia.org/wiki/Metonymy