Is hard to become fluent in Brasilian Portuguese ?

FWIW I've passed the Celpe-Bras exam, and can watch videos, read, and communicate verbally with pretty much anyone here like a native, except people from Bahia KKKKKK, and when encountering regionalized slang. The reason I am asking this question, is that each person learns at their own pace, many of us have all had languages other than the english in our vocabulary, and some have better assimilation and quicker learning curves with languages than others.

So, what brought about this question ?

Well, surfing the web this morning, I got this ad for a language service that quoted a chart from the "US Foreign Service Institute" (which is a legit organization) indicating several different prominent languages, and displaying their categorizations, as to how long it takes to learn each of them to what they state as "proficiency". This word was not clearly defined however, but some vague reference was made to fluency. How that was exactly structured is unexplained though.

Portuguese was in level 1, that is, the easiest to learn, supposedly taking by their standard some 6-7 months of learning using a 40 hour week class schedule. I find that impossible to believe, given my own personal experience with Portuguese, and, that I have been fluent in multiple languages in my life, some of them which they indicate on this chart will require a learning timeline of 9 months to 11 months, yet, when I went to school for YEARS, yes, years, to learn them while living in their native countries......heh.

How hard is it to realistically become fluent in Brasilian Portuguese  in your opinion ?