Merriam-Webster is taking the distinctly minority view on this, when it comes to dictionaries. When it comes to actual usage, something being "no longer widely seen as incorrect" is not quite the ringing validation for any common mistake of the masses that you seem to think it is.

A much better writeup with a listing of many dictionaries and grammar guides that take the correct approach is here:

https://www.grammarphobia.com/blog/2017/06/flaunt-flout.html