Your comment that “without adequate knowledge of English grammar rules, learners often cannot create their own grammatically correct sentences, and often cannot understand what they read or listen to in English” completely ignores how the brain works. The human brain is hard wired to figure out the grammatical patterns in the language (or languages) it encounters if given enough input. You did not learn your native language of English through conscious study of English grammar, and nor is such study necessary for learning a foreign language. That said, I do think that adult learners can get some benefit from looking at the basic structures of their target language, but grammar rules are of little use until one has received enough exposure to the language.

Grammar books with explanations and exercises have been published by
knowledgeable language specialists to make learning grammar easier so
that learners don’t have to discover grammar rules anew the hard long
way.

I’ve received some messages from people advocating unconventional
English learning methods and promoting English learning products of that
kind. I’ve explored some of their websites that contain a number of
learners’ comments. Supporters of unconventional learning methods and
products claim that learning grammar is unnecessary and inhibits fluent
speaking.

A growing number of learners are misled and lose time experiencing delay
in language learning progress because of superficial claims of
promoters of unconventional English learning methods and products.

I disagree with those speculative claims as knowing grammar rules
logically reduces making mistakes by learners. Without adequate knowledge of English grammar rules learners often cannot create their own grammatically correct sentences, and often cannot understand what they read or listen to in English exactly.

Conventional communicative
English teaching and learning supported with adequate regular long-term
practice in listening comprehension and speaking English yield effective
results. Lack of such practice in English by learners produces speculations that
conventional English learning and teaching methods don’t work.