Like I posted to elsie, then what about galatians 1:6 8 and 9 contains the exact same thing. You may be ticky tacky right about the verse being incorrect but the admonition is true and was laid down in both OT and NT. Are you just saying that revelations is incorrect for the premise or that the premise is wrong?
If you read my original post to faucetman on the topic, you’ll see that I agree that there is a prohibition on adding to the Gospel. I just don’t like it when people mis-cite that verse from Revelation as justification for that argument. There are better verses, as you have cited, that serve the purpose, so there is no need to twist the one from Revelation to fit.