In the irrelevant and humble opinion of the author of these lines in Portuguese there are much more intransparent conjunctions than in other languages, at least this author has never observed that in any other language. By intransparent we mean conjunctions whose components suggests a different meaning from the one they actually have.
Who reads contanto associate it with com tanto, what would be so much / so many and that has nothing to do with the actual meaning of contanto. Tanto / tanta / tantos / tantas is an adjective.
Por que há tantas pessoas infelizes? <=> Why there are so many unhappy people.
Ninguém ganha tanto dinheiro como eles. <=> Nobody earns as much money as they do.
The construction con tanto que, written separated, in the sense of provided that existed in Spanish as well in the 16th century, but was eliminated in the course of history.
Com tanto exists in Portuguese as well and then it means what is suggests.
com tanto que
Com tanto que há para fazer, tive de trabalhar mais.
Given all the things he still has to do, he has to work more.
The next question is how relevant is this conjunction. One would assume that this conjunction is rarely used, because there are a lot of alternative, suposto que, caso que, se, but this is wrong. With contudo we get 560 000 results in a search engine and the much more transparent suposto que yields only 130 000 results. That is not a lot in comparison to caso que with 22 millions results, but still a lot.
contanto que provided that
Eu ensino-te contanto que estejas com atenção.
I show it to you, provided that you pay attention.
Você pode vir, contanto que você pare de me irritar.
You can come, provided that you stop bothering me.
Você pode ficar, contanto que trabalhe.
You can stay, provided that you work.
Você vai aprender inglês, contanto que você pratique muito.
You will lern english, provided that you practise it.