American English is not 'dumb'; it's just a different type of British English. And British English certainly isn't the gold standard, or the more 'correct' English. It's pretty snobby to think that American English is inferior to other types of English.
There are plenty of grammar guides out there. The "Oxford Modern English Grammar" is very detailed and linguistic-y (sometimes too detailed, but depends what you need it for really). There are more practical reference guides like Swan's "Practical English Usage" which is a bit more accessible.