It would have come across as less rude if it had been prefaced with something to the effect of "I found your post insightful because xyz. It appears that you're

It would have come across as less rude if it had been prefaced with something to the effect of "I found your post insightful because xyz. It appears that you're not a native English speaker. In case you might find it helpful, I've made some suggestions below to improve the grammar of your post to make it more accessible to other readers."