I can give you an e.g. by one of the greats of all time.. Scrivener.. he did not want any of his comp. couples going to other teachers, and he made this quite clear ( thats not to say they didnt! )
There is much conflict in theory in the higher ( and sometimes lower )echelons of Standard for e.g.
Much depends on the style wants to adopt ( Italian, English etc. ) in and of themselves, they are not wrong ,but approach the subject matter, in some instances, from a different view point, which can be in conflict with other top Pros theories.
The major problem for beginners ?.. discernment.. at the outset, they do not have the knowledge to evaluate their current teacher, and will, in most cases, defend their teaching at any cost.
The abilty to convey information ( teaching ) is a skill that develops with time and guidance in the hands of well seasoned Prof.