Hiding behind passive constructions doesn't change the fundamental message. Somebody is using the language and taking (or not) the level of care you believe is called for, so it reflects on them regardless of how you phrase it.

It's your community, but to this native English speaker the phrasing in your criticism comes across as rude. You could have easily changed the feel of the entire response by omitting the  "[...use of language is sloppy, and a bit more care could have really upgraded the quality of this post...]" completely, and it would seem much more friendly and encouraging while communicating the same point.

I'll leave it here, since as I said, it's your community. I do enjoy the posts and appreciate the gatekeeping for the most part!