What you are saying is generally true (and certainly true for many Indian texts), but the oral tradition of the Vedas really is old. Having been brought up in the West I only learned enough for daily and occasional rituals. My guru taught me without looking at a book and although I have such books now I bought them for curiosity only; if I had a question about recitation it would not occur to me to consult them. My son has learned the same way.

Could be but all across different regions across the subcontinent where the Vedas are orally recited, except for some technical tones and notes (which is the mechanical part of Vedic Sanskrit) there is little difference.

There are serious attempts made to write down the vedas. The thing is, historically, very few people learned all 4 vedas by heart; Instead different families recited very small part and passed the recitation as heirloom.

If you meet all those families and compile their recitation, it exactly matches to what we have from different earlier efforts of canonisation.