Re: La gramática más compleja
Nice metaphor, Palomnik.
And I agree that Slavic languages are ultimately violin languages - except for Bulgarian and Macedonian because you still are able to communicate successfully even without correct use of the complex time system.
Well, there's still aspect but if you concentrate on present tense this is not too complicated; and if you get verbal aspect wrong misunderstandings may be the result, but many times context will allow native speakers to understand what you really meant.
But if you get all the cases wrong (in those Slavic languages which rely hugely on declension) communication may even fail or will be at least very difficult.
German is somewhere in-between though; with the main problem not being declension but word order and syntax - a huge problem for many learners.
But I wouldn't go so far as to say that piano languages don't have complex grammars - they only have different ones: e. g. phrasal verbs in English, they also are part of grammar (which most beginners of English don't even realise; I certainly didn't - probably because my teachers thought that they rather belong to the lexicon than grammar).
Well, I think your metaphor of piano and violin already provides for that: you may be quick to pick up the basics of piano, but if you want to become a master you have to work really hard on your skills, only this comes at a later stage while with violin you will have to do some very hard work right at the beginning.
"An esoteric may claim more nonsense in 5 minutes than a scientist may be able to disprove in his entire life." Vince Ebert, about fighting sciolism.