Can't backup DB locally with MAMP PRO 5.5.1
I have run the following on my computer in order to allow Mac OS's terminal to speak to MAMP's MySQL. I have not done the steps outlined in your linked article. Craft's built-in backup tool works fine for me so perhaps this will help you too.

sudo ln -s /Applications/MAMP/Library/bin/mysqldump /usr/local/bin/mysqldump


Here's a github issue on the matter that runs through a few possible solutions (including the one above).