Thanks for the helpful comments and the links. To my understanding, the gradual training outlined in some early discourses starting from the training of sila were meant for the "learners" (the 1st type of noble monastic disciples), who had already heard the Dhamma and gained the faith in the Buddha:
"In the same way, brahman, there is the case where a Tathagata appears in the world, worthy and rightly self-awakened. He teaches the Dhamma admirable in its beginning, admirable in its middle, admirable in its end. He proclaims the holy life both in its particulars and in its essence, entirely perfect, surpassingly pure.
"A householder or householder's son, hearing the Dhamma, gains faith in the Tathagata
and reflects: 'Household life is confining, a dusty path. Life gone forth is the open air. It isn't easy, living at home, to practice the holy life totally perfect, totally pure, a polished shell. What if I, having shaved off my hair & beard and putting on the ochre robe, were to go forth from the household life into homelessness?'
"So after some time he abandons his mass of wealth, large or small; leaves his circle of relatives, large or small; shaves off his hair and beard, puts on the ochre robes, and goes forth from the household life into homelessness.”
“When he has thus gone forth
, endowed with the monks' training & livelihood, then …" (start training on sila)
"Brahman, such is my instruction for those monks who are learners
who, perfection being not yet attained, dwell longing for the incomparable security from the bonds.”
Visuddhimagga might be intended for such learners as well. At least in the Buddha's time, the monks started their training as learners, because they had gone forth because of their faith on the Teaching. This might also apply to the time of Ven. Buddhagosa. If that's the case, the missing of "hearing the Dhamma" from Visuddhimagga is not to be blamed. But it would be better to make it clear that the commentory is meant for the "learners" only, that it is only to be used as a reference book for the Teaching and the practitioners should follow the Teaching (suttas) instead. I agree that there are different ways that practitioners have developed the path. It appears to me that the Buddha had taught different ways as well.
His early teachings such as MN 107 and MN 27 appear to have taught the way how he was practicing and becoming enlightened. I couldn't find the complete set of training on mindfulness of body/ feeling/mind states/Dhamma as outlined in MN 10 (and then MN 118) in these early suttas. I suppose that the practitioners with very little dust in their eyes and possessing very keen faculties and good mastery of samadhi (jhanas) could become enlightened that way.
It appears to me that the later discourses (e.g. MN 10, MN 118, the suttas on dependent origination) taught more methods for developing the path, to suit different practitioners with different faculties/"illnesses". These methods, such as those taught in MN 10 for establishing the FOUR mindfulness, are very effective. It would be a pity not to incorporate them in the training.
Just some food for thought. Thanks and metta!