This statement is very strange, as not accurate.
At times, global variables are all you need for specific mechanics. I've used them in most of my videos in the C2 Academy and it makes sense, more than using a dictionary.
At other times, local variables are just perfect when nested in a function or a specific block of sub-events and are all which is required. Dictionaries would actually make less sense at that moment.
Unless you could add some specific case of use, I disagree and counter-advice what this topic is saying.
Also I've always preferred arrays to dictionary anyway.
So in the end, my advice would be use what you feel more comfortable with and what makes sense in your project/mechanic.
I agree that it's probably best to use a data structure rather than dozens of global variables for some data usage, but again, that's not necessary what the OP seems to hint at.